dom/imptests/testharness.js

/*
Distributed under both the W3C Test Suite License [1] and the W3C
3-clause BSD License [2]. To contribute to a W3C Test Suite, see the
policies and contribution forms [3].

[1] http://www.w3.org/Consortium/Legal/2008/04-testsuite-license
[2] http://www.w3.org/Consortium/Legal/2008/03-bsd-license
[3] http://www.w3.org/2004/10/27-testcases
*/

/*
 * == Introduction ==
 *
 * This file provides a framework for writing testcases. It is intended to
 * provide a convenient API for making common assertions, and to work both
 * for testing synchronous and asynchronous DOM features in a way that
 * promotes clear, robust, tests.
 *
 * == Basic Usage ==
 *
 * To use this file, import the script and the testharnessreport script into
 * the test document:
 * <script src="/resources/testharness.js"></script>
 * <script src="/resources/testharnessreport.js"></script>
 *
 * Within each file one may define one or more tests. Each test is atomic
 * in the sense that a single test has a single result (pass/fail/timeout).
 * Within each test one may have a number of asserts. The test fails at the
 * first failing assert, and the remainder of the test is (typically) not run.
 *
 * If the file containing the tests is a HTML file with an element of id "log"
 * this will be populated with a table containing the test results after all
 * the tests have run.
 *
 * NOTE: By default tests must be created before the load event fires. For ways
 *       to create tests after the load event, see "Determining when all tests
 *       are complete", below
 *
 * == Synchronous Tests ==
 *
 * To create a synchronous test use the test() function:
 *
 * test(test_function, name, properties)
 *
 * test_function is a function that contains the code to test. For example a
 * trivial passing test would be:
 *
 * test(function() {assert_true(true)}, "assert_true with true")
 *
 * The function passed in is run in the test() call.
 *
 * properties is an object that overrides default test properties. The
 * recognised properties are:
 *    timeout - the test timeout in ms
 *
 * e.g.
 * test(test_function, "Sample test", {timeout:1000})
 *
 * would run test_function with a timeout of 1s.
 *
 * Additionally, test-specific metadata can be passed in the properties. These
 * are used when the individual test has different metadata from that stored 
 * in the <head>.
 * The recognized metadata properties are:
 *
 *    help - The url of the part of the specification being tested
 *
 *    assert - A human readable description of what the test is attempting 
 *             to prove
 *
 *    author - Name and contact information for the author of the test in the
 *             format: "Name <email_addr>" or "Name http://contact/url"
 *
 *    flags - space separated list of test flags in addition to any present in
 *            the head metadata
 *
 * == Asynchronous Tests ==
 *
 * Testing asynchronous features is somewhat more complex since the result of
 * a test may depend on one or more events or other callbacks. The API provided
 * for testing these features is indended to be rather low-level but hopefully
 * applicable to many situations.
 *
 * To create a test, one starts by getting a Test object using async_test:
 *
 * async_test(name, properties)
 *
 * e.g.
 * var t = async_test("Simple async test")
 *
 * Assertions can be added to the test by calling the step method of the test
 * object with a function containing the test assertions:
 *
 * t.step(function() {assert_true(true)});
 *
 * When all the steps are complete, the done() method must be called:
 *
 * t.done();
 *
 * As a convenience, async_test can also takes a function as first argument.
 * This function is called with the test object as both its `this` object and
 * first argument. The above example can be rewritten as:
 *
 * async_test(function(t) {
 *     object.some_event = function() {
 *         t.step(function (){assert_true(true); t.done();});
 *     };
 * }, "Simple async test");
 *
 * which avoids cluttering the global scope with references to async
 * tests instances.
 *
 * The properties argument is identical to that for test().
 *
 * In many cases it is convenient to run a step in response to an event or a
 * callback. A convenient method of doing this is through the step_func method
 * which returns a function that, when called runs a test step. For example
 *
 * object.some_event = t.step_func(function(e) {assert_true(e.a)});
 *
 * == Making assertions ==
 *
 * Functions for making assertions start assert_
 * The best way to get a list is to look in this file for functions names
 * matching that pattern. The general signature is
 *
 * assert_something(actual, expected, description)
 *
 * although not all assertions precisely match this pattern e.g. assert_true
 * only takes actual and description as arguments.
 *
 * The description parameter is used to present more useful error messages when
 * a test fails
 *
 * NOTE: All asserts must be located in a test() or a step of an async_test().
 *       asserts outside these places won't be detected correctly by the harness
 *       and may cause a file to stop testing.
 *
 * == Setup ==
 *
 * Sometimes tests require non-trivial setup that may fail. For this purpose
 * there is a setup() function, that may be called with one or two arguments.
 * The two argument version is:
 *
 * setup(func, properties)
 *
 * The one argument versions may omit either argument.
 * func is a function to be run synchronously. setup() becomes a no-op once
 * any tests have returned results. Properties are global properties of the test
 * harness. Currently recognised properties are:
 *
 * timeout - The time in ms after which the harness should stop waiting for
 *           tests to complete (this is different to the per-test timeout
 *           because async tests do not start their timer until .step is called)
 *
 * explicit_done - Wait for an explicit call to done() before declaring all
 *                 tests complete (see below)
 *
 * output_document - The document to which results should be logged. By default
 *                   this is the current document but could be an ancestor
 *                   document in some cases e.g. a SVG test loaded in an HTML
 *                   wrapper
 *
 * explicit_timeout - disable file timeout; only stop waiting for results
 *                    when the timeout() function is called (typically for
 *                    use when integrating with some existing test framework
 *                    that has its own timeout mechanism).
 *
 * == Determining when all tests are complete ==
 *
 * By default the test harness will assume there are no more results to come
 * when:
 * 1) There are no Test objects that have been created but not completed
 * 2) The load event on the document has fired
 *
 * This behaviour can be overridden by setting the explicit_done property to
 * true in a call to setup(). If explicit_done is true, the test harness will
 * not assume it is done until the global done() function is called. Once done()
 * is called, the two conditions above apply like normal.
 *
 * == Generating tests ==
 *
 * NOTE: this functionality may be removed
 *
 * There are scenarios in which is is desirable to create a large number of
 * (synchronous) tests that are internally similar but vary in the parameters
 * used. To make this easier, the generate_tests function allows a single
 * function to be called with each set of parameters in a list:
 *
 * generate_tests(test_function, parameter_lists, properties)
 *
 * For example:
 *
 * generate_tests(assert_equals, [
 *     ["Sum one and one", 1+1, 2],
 *     ["Sum one and zero", 1+0, 1]
 *     ])
 *
 * Is equivalent to:
 *
 * test(function() {assert_equals(1+1, 2)}, "Sum one and one")
 * test(function() {assert_equals(1+0, 1)}, "Sum one and zero")
 *
 * Note that the first item in each parameter list corresponds to the name of
 * the test.
 *
 * The properties argument is identical to that for test(). This may be a 
 * single object (used for all generated tests) or an array.
 *
 * == Callback API ==
 *
 * The framework provides callbacks corresponding to 3 events:
 *
 * start - happens when the first Test is created
 * result - happens when a test result is recieved
 * complete - happens when all results are recieved
 *
 * The page defining the tests may add callbacks for these events by calling
 * the following methods:
 *
 *   add_start_callback(callback) - callback called with no arguments
 *   add_result_callback(callback) - callback called with a test argument
 *   add_completion_callback(callback) - callback called with an array of tests
 *                                       and an status object
 *
 * tests have the following properties:
 *   status: A status code. This can be compared to the PASS, FAIL, TIMEOUT and
 *           NOTRUN properties on the test object
 *   message: A message indicating the reason for failure. In the future this
 *            will always be a string
 *
 *  The status object gives the overall status of the harness. It has the
 *  following properties:
 *    status: Can be compared to the OK, ERROR and TIMEOUT properties
 *    message: An error message set when the status is ERROR
 *
 * == External API ==
 *
 * In order to collect the results of multiple pages containing tests, the test
 * harness will, when loaded in a nested browsing context, attempt to call
 * certain functions in each ancestor and opener browsing context:
 *
 * start - start_callback
 * result - result_callback
 * complete - completion_callback
 *
 * These are given the same arguments as the corresponding internal callbacks
 * described above.
 *
 * == External API through cross-document messaging ==
 *
 * Where supported, the test harness will also send messages using
 * cross-document messaging to each ancestor and opener browsing context. Since
 * it uses the wildcard keyword (*), cross-origin communication is enabled and
 * script on different origins can collect the results.
 *
 * This API follows similar conventions as those described above only slightly
 * modified to accommodate message event API. Each message is sent by the harness
 * is passed a single vanilla object, available as the `data` property of the
 * event object. These objects are structures as follows:
 *
 * start - { type: "start" }
 * result - { type: "result", test: Test }
 * complete - { type: "complete", tests: [Test, ...], status: TestsStatus }
 *
 * == List of assertions ==
 *
 * assert_true(actual, description)
 *   asserts that /actual/ is strictly true
 *
 * assert_false(actual, description)
 *   asserts that /actual/ is strictly false
 *
 * assert_equals(actual, expected, description)
 *   asserts that /actual/ is the same value as /expected/
 *
 * assert_not_equals(actual, expected, description)
 *   asserts that /actual/ is a different value to /expected/. Yes, this means
 *   that "expected" is a misnomer
 *
 * assert_in_array(actual, expected, description)
 *   asserts that /expected/ is an Array, and /actual/ is equal to one of the
 *   members -- expected.indexOf(actual) != -1
 *
 * assert_array_equals(actual, expected, description)
 *   asserts that /actual/ and /expected/ have the same length and the value of
 *   each indexed property in /actual/ is the strictly equal to the corresponding
 *   property value in /expected/
 *
 * assert_approx_equals(actual, expected, epsilon, description)
 *   asserts that /actual/ is a number within +/- /epsilon/ of /expected/
 *
 * assert_regexp_match(actual, expected, description)
 *   asserts that /actual/ matches the regexp /expected/
 *
 * assert_class_string(object, class_name, description)
 *   asserts that the class string of /object/ as returned in
 *   Object.prototype.toString is equal to /class_name/.
 *
 * assert_own_property(object, property_name, description)
 *   assert that object has own property property_name
 *
 * assert_inherits(object, property_name, description)
 *   assert that object does not have an own property named property_name
 *   but that property_name is present in the prototype chain for object
 *
 * assert_idl_attribute(object, attribute_name, description)
 *   assert that an object that is an instance of some interface has the
 *   attribute attribute_name following the conditions specified by WebIDL
 *
 * assert_readonly(object, property_name, description)
 *   assert that property property_name on object is readonly
 *
 * assert_throws(code, func, description)
 *   code - the expected exception:
 *     o string: the thrown exception must be a DOMException with the given
 *               name, e.g., "TimeoutError" (for compatibility with existing
 *               tests, a constant is also supported, e.g., "TIMEOUT_ERR")
 *     o object: the thrown exception must have a property called "name" that
 *               matches code.name
 *     o null:   allow any exception (in general, one of the options above
 *               should be used)
 *   func - a function that should throw
 *
 * assert_unreached(description)
 *   asserts if called. Used to ensure that some codepath is *not* taken e.g.
 *   an event does not fire.
 *
 * assert_any(assert_func, actual, expected_array, extra_arg_1, ... extra_arg_N)
 *   asserts that one assert_func(actual, expected_array_N, extra_arg1, ..., extra_arg_N)
 *   is true for some expected_array_N in expected_array. This only works for assert_func
 *   with signature assert_func(actual, expected, args_1, ..., args_N). Note that tests
 *   with multiple allowed pass conditions are bad practice unless the spec specifically
 *   allows multiple behaviours. Test authors should not use this method simply to hide 
 *   UA bugs.
 *
 * assert_exists(object, property_name, description)
 *   *** deprecated ***
 *   asserts that object has an own property property_name
 *
 * assert_not_exists(object, property_name, description)
 *   *** deprecated ***
 *   assert that object does not have own property property_name
 */

(function ()
{
    var debug = false;
    // default timeout is 5 seconds, test can override if needed
    var settings = {
      output:true,
      timeout:5000,
      test_timeout:2000
    };

    var xhtml_ns = "http://www.w3.org/1999/xhtml";

    // script_prefix is used by Output.prototype.show_results() to figure out
    // where to get testharness.css from.  It's enclosed in an extra closure to
    // not pollute the library's namespace with variables like "src".
    var script_prefix = null;
    (function ()
    {
        var scripts = document.getElementsByTagName("script");
        for (var i = 0; i < scripts.length; i++)
        {
            if (scripts[i].src)
            {
                var src = scripts[i].src;
            }
            else if (scripts[i].href)
            {
                //SVG case
                var src = scripts[i].href.baseVal;
            }
            if (src && src.slice(src.length - "testharness.js".length) === "testharness.js")
            {
                script_prefix = src.slice(0, src.length - "testharness.js".length);
                break;
            }
        }
    })();

    /*
     * API functions
     */

    var name_counter = 0;
    function next_default_name()
    {
        //Don't use document.title to work around an Opera bug in XHTML documents
        var prefix = document.getElementsByTagName("title").length > 0 ?
                         document.getElementsByTagName("title")[0].firstChild.data :
                         "Untitled";
        var suffix = name_counter > 0 ? " " + name_counter : "";
        name_counter++;
        return prefix + suffix;
    }

    function test(func, name, properties)
    {
        var test_name = name ? name : next_default_name();
        properties = properties ? properties : {};
        var test_obj = new Test(test_name, properties);
        test_obj.step(func);
        if (test_obj.status === test_obj.NOTRUN) {
            test_obj.done();
        }
    }

    function async_test(func, name, properties)
    {
        if (typeof func !== "function") {
            properties = name;
            name = func;
            func = null;
        }
        var test_name = name ? name : next_default_name();
        properties = properties ? properties : {};
        var test_obj = new Test(test_name, properties);
        if (func) {
            test_obj.step(func, test_obj, test_obj);
        }
        return test_obj;
    }

    function setup(func_or_properties, maybe_properties)
    {
        var func = null;
        var properties = {};
        if (arguments.length === 2) {
            func = func_or_properties;
            properties = maybe_properties;
        } else if (func_or_properties instanceof Function){
            func = func_or_properties;
        } else {
            properties = func_or_properties;
        }
        tests.setup(func, properties);
        output.setup(properties);
    }

    function done() {
        tests.end_wait();
    }

    function generate_tests(func, args, properties) {
        forEach(args, function(x, i)
                {
                    var name = x[0];
                    test(function()
                         {
                             func.apply(this, x.slice(1));
                         }, 
                         name, 
                         Array.isArray(properties) ? properties[i] : properties);
                });
    }

    function on_event(object, event, callback)
    {
      object.addEventListener(event, callback, false);
    }

    expose(test, 'test');
    expose(async_test, 'async_test');
    expose(generate_tests, 'generate_tests');
    expose(setup, 'setup');
    expose(done, 'done');
    expose(on_event, 'on_event');

    /*
     * Return a string truncated to the given length, with ... added at the end
     * if it was longer.
     */
    function truncate(s, len)
    {
        if (s.length > len) {
            return s.substring(0, len - 3) + "...";
        }
        return s;
    }

    /*
     * Convert a value to a nice, human-readable string
     */
    function format_value(val)
    {
        if (Array.isArray(val))
        {
            return "[" + val.map(format_value).join(", ") + "]";
        }

        switch (typeof val)
        {
        case "string":
            val = val.replace("\\", "\\\\");
            for (var i = 0; i < 32; i++)
            {
                var replace = "\\";
                switch (i) {
                case 0: replace += "0"; break;
                case 1: replace += "x01"; break;
                case 2: replace += "x02"; break;
                case 3: replace += "x03"; break;
                case 4: replace += "x04"; break;
                case 5: replace += "x05"; break;
                case 6: replace += "x06"; break;
                case 7: replace += "x07"; break;
                case 8: replace += "b"; break;
                case 9: replace += "t"; break;
                case 10: replace += "n"; break;
                case 11: replace += "v"; break;
                case 12: replace += "f"; break;
                case 13: replace += "r"; break;
                case 14: replace += "x0e"; break;
                case 15: replace += "x0f"; break;
                case 16: replace += "x10"; break;
                case 17: replace += "x11"; break;
                case 18: replace += "x12"; break;
                case 19: replace += "x13"; break;
                case 20: replace += "x14"; break;
                case 21: replace += "x15"; break;
                case 22: replace += "x16"; break;
                case 23: replace += "x17"; break;
                case 24: replace += "x18"; break;
                case 25: replace += "x19"; break;
                case 26: replace += "x1a"; break;
                case 27: replace += "x1b"; break;
                case 28: replace += "x1c"; break;
                case 29: replace += "x1d"; break;
                case 30: replace += "x1e"; break;
                case 31: replace += "x1f"; break;
                }
                val = val.replace(RegExp(String.fromCharCode(i), "g"), replace);
            }
            return '"' + val.replace(/"/g, '\\"') + '"';
        case "boolean":
        case "undefined":
            return String(val);
        case "number":
            // In JavaScript, -0 === 0 and String(-0) == "0", so we have to
            // special-case.
            if (val === -0 && 1/val === -Infinity)
            {
                return "-0";
            }
            return String(val);
        case "object":
            if (val === null)
            {
                return "null";
            }

            // Special-case Node objects, since those come up a lot in my tests.  I
            // ignore namespaces.  I use duck-typing instead of instanceof, because
            // instanceof doesn't work if the node is from another window (like an
            // iframe's contentWindow):
            // http://www.w3.org/Bugs/Public/show_bug.cgi?id=12295
            if ("nodeType" in val
            && "nodeName" in val
            && "nodeValue" in val
            && "childNodes" in val)
            {
                switch (val.nodeType)
                {
                case Node.ELEMENT_NODE:
                    var ret = "<" + val.tagName.toLowerCase();
                    for (var i = 0; i < val.attributes.length; i++)
                    {
                        ret += " " + val.attributes[i].name + '="' + val.attributes[i].value + '"';
                    }
                    ret += ">" + val.innerHTML + "</" + val.tagName.toLowerCase() + ">";
                    return "Element node " + truncate(ret, 60);
                case Node.TEXT_NODE:
                    return 'Text node "' + truncate(val.data, 60) + '"';
                case Node.PROCESSING_INSTRUCTION_NODE:
                    return "ProcessingInstruction node with target " + format_value(truncate(val.target, 60)) + " and data " + format_value(truncate(val.data, 60));
                case Node.COMMENT_NODE:
                    return "Comment node <!--" + truncate(val.data, 60) + "-->";
                case Node.DOCUMENT_NODE:
                    return "Document node with " + val.childNodes.length + (val.childNodes.length == 1 ? " child" : " children");
                case Node.DOCUMENT_TYPE_NODE:
                    return "DocumentType node";
                case Node.DOCUMENT_FRAGMENT_NODE:
                    return "DocumentFragment node with " + val.childNodes.length + (val.childNodes.length == 1 ? " child" : " children");
                default:
                    return "Node object of unknown type";
                }
            }

            // Fall through to default
        default:
            return typeof val + ' "' + truncate(String(val), 60) + '"';
        }
    }
    expose(format_value, "format_value");

    /*
     * Assertions
     */

    function assert_true(actual, description)
    {
        assert(actual === true, "assert_true", description,
                                "expected true got ${actual}", {actual:actual});
    };
    expose(assert_true, "assert_true");

    function assert_false(actual, description)
    {
        assert(actual === false, "assert_false", description,
                                 "expected false got ${actual}", {actual:actual});
    };
    expose(assert_false, "assert_false");

    function same_value(x, y) {
        if (y !== y)
        {
            //NaN case
            return x !== x;
        }
        else if (x === 0 && y === 0) {
            //Distinguish +0 and -0
            return 1/x === 1/y;
        }
        else
        {
            //typical case
            return x === y;
        }
    }

    function assert_equals(actual, expected, description)
    {
         /*
          * Test if two primitives are equal or two objects
          * are the same object
          */
        if (typeof actual != typeof expected)
        {
            assert(false, "assert_equals", description,
                          "expected (" + typeof expected + ") ${expected} but got (" + typeof actual + ") ${actual}",
                          {expected:expected, actual:actual});
            return;
        }
        assert(same_value(actual, expected), "assert_equals", description,
                                             "expected ${expected} but got ${actual}",
                                             {expected:expected, actual:actual});
    };
    expose(assert_equals, "assert_equals");

    function assert_not_equals(actual, expected, description)
    {
         /*
          * Test if two primitives are unequal or two objects
          * are different objects
          */
        assert(!same_value(actual, expected), "assert_not_equals", description,
                                              "got disallowed value ${actual}",
                                              {actual:actual});
    };
    expose(assert_not_equals, "assert_not_equals");

    function assert_in_array(actual, expected, description)
    {
        assert(expected.indexOf(actual) != -1, "assert_in_array", description,
                                               "value ${actual} not in array ${expected}",
                                               {actual:actual, expected:expected});
    }
    expose(assert_in_array, "assert_in_array");

    function assert_object_equals(actual, expected, description)
    {
         //This needs to be improved a great deal
         function check_equal(actual, expected, stack)
         {
             stack.push(actual);

             var p;
             for (p in actual)
             {
                 assert(expected.hasOwnProperty(p), "assert_object_equals", description,
                                                    "unexpected property ${p}", {p:p});

                 if (typeof actual[p] === "object" && actual[p] !== null)
                 {
                     if (stack.indexOf(actual[p]) === -1)
                     {
                         check_equal(actual[p], expected[p], stack);
                     }
                 }
                 else
                 {
                     assert(same_value(actual[p], expected[p]), "assert_object_equals", description,
                                                       "property ${p} expected ${expected} got ${actual}",
                                                       {p:p, expected:expected, actual:actual});
                 }
             }
             for (p in expected)
             {
                 assert(actual.hasOwnProperty(p),
                        "assert_object_equals", description,
                        "expected property ${p} missing", {p:p});
             }
             stack.pop();
         }
         check_equal(actual, expected, []);
    };
    expose(assert_object_equals, "assert_object_equals");

    function assert_array_equals(actual, expected, description)
    {
        assert(actual.length === expected.length,
               "assert_array_equals", description,
               "lengths differ, expected ${expected} got ${actual}",
               {expected:expected.length, actual:actual.length});

        for (var i=0; i < actual.length; i++)
        {
            assert(actual.hasOwnProperty(i) === expected.hasOwnProperty(i),
                   "assert_array_equals", description,
                   "property ${i}, property expected to be $expected but was $actual",
                   {i:i, expected:expected.hasOwnProperty(i) ? "present" : "missing",
                   actual:actual.hasOwnProperty(i) ? "present" : "missing"});
            assert(same_value(expected[i], actual[i]),
                   "assert_array_equals", description,
                   "property ${i}, expected ${expected} but got ${actual}",
                   {i:i, expected:expected[i], actual:actual[i]});
        }
    }
    expose(assert_array_equals, "assert_array_equals");

    function assert_approx_equals(actual, expected, epsilon, description)
    {
        /*
         * Test if two primitive numbers are equal withing +/- epsilon
         */
        assert(typeof actual === "number",
               "assert_approx_equals", description,
               "expected a number but got a ${type_actual}",
               {type_actual:typeof actual});

        assert(Math.abs(actual - expected) <= epsilon,
               "assert_approx_equals", description,
               "expected ${expected} +/- ${epsilon} but got ${actual}",
               {expected:expected, actual:actual, epsilon:epsilon});
    };
    expose(assert_approx_equals, "assert_approx_equals");

    function assert_regexp_match(actual, expected, description) {
        /*
         * Test if a string (actual) matches a regexp (expected)
         */
        assert(expected.test(actual),
               "assert_regexp_match", description,
               "expected ${expected} but got ${actual}",
               {expected:expected, actual:actual});
    }
    expose(assert_regexp_match, "assert_regexp_match");

    function assert_class_string(object, class_string, description) {
        assert_equals({}.toString.call(object), "[object " + class_string + "]",
                      description);
    }
    expose(assert_class_string, "assert_class_string");


    function _assert_own_property(name) {
        return function(object, property_name, description)
        {
            assert(object.hasOwnProperty(property_name),
                   name, description,
                   "expected property ${p} missing", {p:property_name});
        };
    }
    expose(_assert_own_property("assert_exists"), "assert_exists");
    expose(_assert_own_property("assert_own_property"), "assert_own_property");

    function assert_not_exists(object, property_name, description)
    {
        assert(!object.hasOwnProperty(property_name),
               "assert_not_exists", description,
               "unexpected property ${p} found", {p:property_name});
    };
    expose(assert_not_exists, "assert_not_exists");

    function _assert_inherits(name) {
        return function (object, property_name, description)
        {
            assert(typeof object === "object",
                   name, description,
                   "provided value is not an object");

            assert("hasOwnProperty" in object,
                   name, description,
                   "provided value is an object but has no hasOwnProperty method");

            assert(!object.hasOwnProperty(property_name),
                   name, description,
                   "property ${p} found on object expected in prototype chain",
                   {p:property_name});

            assert(property_name in object,
                   name, description,
                   "property ${p} not found in prototype chain",
                   {p:property_name});
        };
    }
    expose(_assert_inherits("assert_inherits"), "assert_inherits");
    expose(_assert_inherits("assert_idl_attribute"), "assert_idl_attribute");

    function assert_readonly(object, property_name, description)
    {
         var initial_value = object[property_name];
         try {
             //Note that this can have side effects in the case where
             //the property has PutForwards
             object[property_name] = initial_value + "a"; //XXX use some other value here?
             assert(same_value(object[property_name], initial_value),
                    "assert_readonly", description,
                    "changing property ${p} succeeded",
                    {p:property_name});
         }
         finally
         {
             object[property_name] = initial_value;
         }
    };
    expose(assert_readonly, "assert_readonly");

    function assert_throws(code, func, description)
    {
        try
        {
            func.call(this);
            assert(false, "assert_throws", description,
                   "${func} did not throw", {func:func});
        }
        catch(e)
        {
            if (e instanceof AssertionError) {
                throw(e);
            }
            if (code === null)
            {
                return;
            }
            if (typeof code === "object")
            {
                assert(typeof e == "object" && "name" in e && e.name == code.name,
                       "assert_throws", description,
                       "${func} threw ${actual} (${actual_name}) expected ${expected} (${expected_name})",
                                    {func:func, actual:e, actual_name:e.name,
                                     expected:code,
                                     expected_name:code.name});
                return;
            }

            var code_name_map = {
                INDEX_SIZE_ERR: 'IndexSizeError',
                HIERARCHY_REQUEST_ERR: 'HierarchyRequestError',
                WRONG_DOCUMENT_ERR: 'WrongDocumentError',
                INVALID_CHARACTER_ERR: 'InvalidCharacterError',
                NO_MODIFICATION_ALLOWED_ERR: 'NoModificationAllowedError',
                NOT_FOUND_ERR: 'NotFoundError',
                NOT_SUPPORTED_ERR: 'NotSupportedError',
                INVALID_STATE_ERR: 'InvalidStateError',
                SYNTAX_ERR: 'SyntaxError',
                INVALID_MODIFICATION_ERR: 'InvalidModificationError',
                NAMESPACE_ERR: 'NamespaceError',
                INVALID_ACCESS_ERR: 'InvalidAccessError',
                TYPE_MISMATCH_ERR: 'TypeMismatchError',
                SECURITY_ERR: 'SecurityError',
                NETWORK_ERR: 'NetworkError',
                ABORT_ERR: 'AbortError',
                URL_MISMATCH_ERR: 'URLMismatchError',
                QUOTA_EXCEEDED_ERR: 'QuotaExceededError',
                TIMEOUT_ERR: 'TimeoutError',
                INVALID_NODE_TYPE_ERR: 'InvalidNodeTypeError',
                DATA_CLONE_ERR: 'DataCloneError'
            };

            var name = code in code_name_map ? code_name_map[code] : code;

            var name_code_map = {
                IndexSizeError: 1,
                HierarchyRequestError: 3,
                WrongDocumentError: 4,
                InvalidCharacterError: 5,
                NoModificationAllowedError: 7,
                NotFoundError: 8,
                NotSupportedError: 9,
                InvalidStateError: 11,
                SyntaxError: 12,
                InvalidModificationError: 13,
                NamespaceError: 14,
                InvalidAccessError: 15,
                TypeMismatchError: 17,
                SecurityError: 18,
                NetworkError: 19,
                AbortError: 20,
                URLMismatchError: 21,
                QuotaExceededError: 22,
                TimeoutError: 23,
                InvalidNodeTypeError: 24,
                DataCloneError: 25,

                UnknownError: 0,
                ConstraintError: 0,
                DataError: 0,
                TransactionInactiveError: 0,
                ReadOnlyError: 0,
                VersionError: 0
            };

            if (!(name in name_code_map))
            {
                throw new AssertionError('Test bug: unrecognized DOMException code "' + code + '" passed to assert_throws()');
            }

            var required_props = { code: name_code_map[name] };

            if (required_props.code === 0
            || ("name" in e && e.name !== e.name.toUpperCase() && e.name !== "DOMException"))
            {
                // New style exception: also test the name property.
                required_props.name = name;
            }

            //We'd like to test that e instanceof the appropriate interface,
            //but we can't, because we don't know what window it was created
            //in.  It might be an instanceof the appropriate interface on some
            //unknown other window.  TODO: Work around this somehow?

            assert(typeof e == "object",
                   "assert_throws", description,
                   "${func} threw ${e} with type ${type}, not an object",
                   {func:func, e:e, type:typeof e});

            for (var prop in required_props)
            {
                assert(typeof e == "object" && prop in e && e[prop] == required_props[prop],
                       "assert_throws", description,
                       "${func} threw ${e} that is not a DOMException " + code + ": property ${prop} is equal to ${actual}, expected ${expected}",
                       {func:func, e:e, prop:prop, actual:e[prop], expected:required_props[prop]});
            }
        }
    }
    expose(assert_throws, "assert_throws");

    function assert_unreached(description) {
         assert(false, "assert_unreached", description,
                "Reached unreachable code");
    }
    expose(assert_unreached, "assert_unreached");

    function assert_any(assert_func, actual, expected_array) 
    {
        var args = [].slice.call(arguments, 3)
        var errors = []
        var passed = false;
        forEach(expected_array, 
                function(expected)
                {
                    try {
                        assert_func.apply(this, [actual, expected].concat(args))
                        passed = true;
                    } catch(e) {
                        errors.push(e.message);
                    }
                });
        if (!passed) {
            throw new AssertionError(errors.join("\n\n"));
        }
    }
    expose(assert_any, "assert_any");

    function Test(name, properties)
    {
        this.name = name;
        this.status = this.NOTRUN;
        this.timeout_id = null;
        this.is_done = false;

        this.properties = properties;
        this.timeout_length = properties.timeout ? properties.timeout : settings.test_timeout;

        this.message = null;

        var this_obj = this;
        this.steps = [];

        tests.push(this);
    }

    Test.statuses = {
        PASS:0,
        FAIL:1,
        TIMEOUT:2,
        NOTRUN:3
    };

    Test.prototype = merge({}, Test.statuses);

    Test.prototype.structured_clone = function()
    {
        if(!this._structured_clone)
        {
            var msg = this.message;
            msg = msg ? String(msg) : msg;
            this._structured_clone = merge({
                name:String(this.name),
                status:this.status,
                message:msg
            }, Test.statuses);
        }
        return this._structured_clone;
    };

    Test.prototype.step = function(func, this_obj)
    {
        //In case the test has already failed
        if (this.status !== this.NOTRUN)
        {
          return;
        }

        tests.started = true;

        if (this.timeout_id === null) {
            this.set_timeout();
        }

        this.steps.push(func);

        if (arguments.length === 1)
        {
            this_obj = this;
        }

        try
        {
            func.apply(this_obj, Array.prototype.slice.call(arguments, 2));
        }
        catch(e)
        {
            //This can happen if something called synchronously invoked another
            //step
            if (this.status !== this.NOTRUN)
            {
                return;
            }
            this.status = this.FAIL;
            this.message = (typeof e === "object" && e !== null) ? e.message : e;
            if (typeof e.stack != "undefined" && typeof e.message == "string") {
                //Try to make it more informative for some exceptions, at least
                //in Gecko and WebKit.  This results in a stack dump instead of
                //just errors like "Cannot read property 'parentNode' of null"
                //or "root is null".  Makes it a lot longer, of course.
                this.message += "(stack: " + e.stack + ")";
            }
            this.done();
            if (debug && e.constructor !== AssertionError) {
                throw e;
            }
        }
    };

    Test.prototype.step_func = function(func, this_obj)
    {
        var test_this = this;

        if (arguments.length === 1)
        {
            this_obj = test_this;
        }

        return function()
        {
            test_this.step.apply(test_this, [func, this_obj].concat(
                Array.prototype.slice.call(arguments)));
        };
    };

    Test.prototype.step_func_done = function(func, this_obj)
    {
        var test_this = this;

        if (arguments.length === 1)
        {
            this_obj = test_this;
        }

        return function()
        {
            test_this.step.apply(test_this, [func, this_obj].concat(
                Array.prototype.slice.call(arguments)));
            test_this.done();
        };
    };

    Test.prototype.set_timeout = function()
    {
        var this_obj = this;
        this.timeout_id = setTimeout(function()
                                     {
                                         this_obj.timeout();
                                     }, this.timeout_length);
    };

    Test.prototype.timeout = function()
    {
        this.status = this.TIMEOUT;
        this.timeout_id = null;
        this.message = "Test timed out";
        this.done();
    };

    Test.prototype.done = function()
    {
        if (this.is_done) {
            return;
        }
        clearTimeout(this.timeout_id);
        if (this.status === this.NOTRUN)
        {
            this.status = this.PASS;
        }
        this.is_done = true;
        tests.result(this);
    };


    /*
     * Harness
     */

    function TestsStatus()
    {
        this.status = null;
        this.message = null;
    }

    TestsStatus.statuses = {
        OK:0,
        ERROR:1,
        TIMEOUT:2
    };

    TestsStatus.prototype = merge({}, TestsStatus.statuses);

    TestsStatus.prototype.structured_clone = function()
    {
        if(!this._structured_clone)
        {
            var msg = this.message;
            msg = msg ? String(msg) : msg;
            this._structured_clone = merge({
                status:this.status,
                message:msg
            }, TestsStatus.statuses);
        }
        return this._structured_clone;
    };

    function Tests()
    {
        this.tests = [];
        this.num_pending = 0;

        this.phases = {
            INITIAL:0,
            SETUP:1,
            HAVE_TESTS:2,
            HAVE_RESULTS:3,
            COMPLETE:4
        };
        this.phase = this.phases.INITIAL;

        this.properties = {};

        //All tests can't be done until the load event fires
        this.all_loaded = false;
        this.wait_for_finish = false;
        this.processing_callbacks = false;

        this.timeout_length = settings.timeout;
        this.timeout_id = null;

        this.start_callbacks = [];
        this.test_done_callbacks = [];
        this.all_done_callbacks = [];

        this.status = new TestsStatus();

        var this_obj = this;

        on_event(window, "load",
                 function()
                 {
                     this_obj.all_loaded = true;
                     if (this_obj.all_done())
                     {
                         this_obj.complete();
                     }
                 });

        this.set_timeout();
    }

    Tests.prototype.setup = function(func, properties)
    {
        if (this.phase >= this.phases.HAVE_RESULTS)
        {
            return;
        }
        if (this.phase < this.phases.SETUP)
        {
            this.phase = this.phases.SETUP;
        }

        for (var p in properties)
        {
            if (properties.hasOwnProperty(p))
            {
                this.properties[p] = properties[p];
            }
        }

        if (properties.timeout)
        {
            this.timeout_length = properties.timeout;
        }
        if (properties.explicit_done)
        {
            this.wait_for_finish = true;
        }
        if (properties.explicit_timeout) {
            this.timeout_length = null;
        }

        if (func)
        {
            try
            {
                func();
            } catch(e)
            {
                this.status.status = this.status.ERROR;
                this.status.message = e;
            };
        }
        this.set_timeout();
    };

    Tests.prototype.set_timeout = function()
    {
        var this_obj = this;
        clearTimeout(this.timeout_id);
        if (this.timeout_length !== null)
        {
            this.timeout_id = setTimeout(function() {
                                             this_obj.timeout();
                                         }, this.timeout_length);
        }
    };

    Tests.prototype.timeout = function() {
        this.status.status = this.status.TIMEOUT;
        this.complete();
    };

    Tests.prototype.end_wait = function()
    {
        this.wait_for_finish = false;
        if (this.all_done()) {
            this.complete();
        }
    };

    Tests.prototype.push = function(test)
    {
        if (this.phase < this.phases.HAVE_TESTS) {
            this.start();
        }
        this.num_pending++;
        this.tests.push(test);
    };

    Tests.prototype.all_done = function() {
        return (this.all_loaded && this.num_pending === 0 &&
                !this.wait_for_finish && !this.processing_callbacks);
    };

    Tests.prototype.start = function() {
        this.phase = this.phases.HAVE_TESTS;
        this.notify_start();
    };

    Tests.prototype.notify_start = function() {
        var this_obj = this;
        forEach (this.start_callbacks,
                 function(callback)
                 {
                     callback(this_obj.properties);
                 });
        forEach_windows(
                function(w, is_same_origin)
                {
                    if(is_same_origin && w.start_callback)
                    {
                        try
                        {
                            w.start_callback(this_obj.properties);
                        }
                        catch(e)
                        {
                            if (debug)
                            {
                                throw(e);
                            }
                        }
                    }
                    if (supports_post_message(w) && w !== self)
                    {
                        w.postMessage({
                            type: "start",
                            properties: this_obj.properties
                        }, "*");
                    }
                });
    };

    Tests.prototype.result = function(test)
    {
        if (this.phase > this.phases.HAVE_RESULTS)
        {
            return;
        }
        this.phase = this.phases.HAVE_RESULTS;
        this.num_pending--;
        this.notify_result(test);
    };

    Tests.prototype.notify_result = function(test) {
        var this_obj = this;
        this.processing_callbacks = true;
        forEach(this.test_done_callbacks,
                function(callback)
                {
                    callback(test, this_obj);
                });

        forEach_windows(
                function(w, is_same_origin)
                {
                    if(is_same_origin && w.result_callback)
                    {
                        try
                        {
                            w.result_callback(test);
                        }
                        catch(e)
                        {
                            if(debug) {
                                throw e;
                            }
                        }
                    }
                    if (supports_post_message(w) && w !== self)
                    {
                        w.postMessage({
                            type: "result",
                            test: test.structured_clone()
                        }, "*");
                    }
                });
        this.processing_callbacks = false;
        if (this_obj.all_done())
        {
            this_obj.complete();
        }
    };

    Tests.prototype.complete = function() {
        if (this.phase === this.phases.COMPLETE) {
            return;
        }
        this.phase = this.phases.COMPLETE;
        var this_obj = this;
        this.tests.forEach(
            function(x)
            {
                if(x.status === x.NOTRUN)
                {
                    this_obj.notify_result(x);
                }
            }
        );
        this.notify_complete();
    };

    Tests.prototype.notify_complete = function()
    {
        clearTimeout(this.timeout_id);
        var this_obj = this;
        var tests = map(this_obj.tests,
                        function(test)
                        {
                            return test.structured_clone();
                        });
        if (this.status.status === null)
        {
            this.status.status = this.status.OK;
        }

        forEach (this.all_done_callbacks,
                 function(callback)
                 {
                     callback(this_obj.tests, this_obj.status);
                 });

        forEach_windows(
                function(w, is_same_origin)
                {
                    if(is_same_origin && w.completion_callback)
                    {
                        try
                        {
                            w.completion_callback(this_obj.tests, this_obj.status);
                        }
                        catch(e)
                        {
                            if (debug)
                            {
                                throw e;
                            }
                        }
                    }
                    if (supports_post_message(w) && w !== self)
                    {
                        w.postMessage({
                            type: "complete",
                            tests: tests,
                            status: this_obj.status.structured_clone()
                        }, "*");
                    }
                });
    };

    var tests = new Tests();

    function timeout() {
        if (tests.timeout_length === null)
        {
            tests.timeout();
        }
    }
    expose(timeout, 'timeout');

    function add_start_callback(callback) {
        tests.start_callbacks.push(callback);
    }

    function add_result_callback(callback)
    {
        tests.test_done_callbacks.push(callback);
    }

    function add_completion_callback(callback)
    {
       tests.all_done_callbacks.push(callback);
    }

    expose(add_start_callback, 'add_start_callback');
    expose(add_result_callback, 'add_result_callback');
    expose(add_completion_callback, 'add_completion_callback');

    /*
     * Output listener
    */

    function Output() {
      this.output_document = document;
      this.output_node = null;
      this.done_count = 0;
      this.enabled = settings.output;
      this.phase = this.INITIAL;
    }

    Output.prototype.INITIAL = 0;
    Output.prototype.STARTED = 1;
    Output.prototype.HAVE_RESULTS = 2;
    Output.prototype.COMPLETE = 3;

    Output.prototype.setup = function(properties) {
        if (this.phase > this.INITIAL) {
            return;
        }

        //If output is disabled in testharnessreport.js the test shouldn't be
        //able to override that
        this.enabled = this.enabled && (properties.hasOwnProperty("output") ?
                                        properties.output : settings.output);
    };

    Output.prototype.init = function(properties)
    {
        if (this.phase >= this.STARTED) {
            return;
        }
        if (properties.output_document) {
            this.output_document = properties.output_document;
        } else {
            this.output_document = document;
        }
        this.phase = this.STARTED;
    };

    Output.prototype.resolve_log = function()
    {
        var output_document;
        if (typeof this.output_document === "function")
        {
            output_document = this.output_document.apply(undefined);
        } else
        {
            output_document = this.output_document;
        }
        if (!output_document)
        {
            return;
        }
        var node = output_document.getElementById("log");
        if (node)
        {
            this.output_document = output_document;
            this.output_node = node;
        }
    };

    Output.prototype.show_status = function(test)
    {
        if (this.phase < this.STARTED)
        {
            this.init();
        }
        if (!this.enabled)
        {
            return;
        }
        if (this.phase < this.HAVE_RESULTS)
        {
            this.resolve_log();
            this.phase = this.HAVE_RESULTS;
        }
        this.done_count++;
        if (this.output_node)
        {
            if (this.done_count < 100
            || (this.done_count < 1000 && this.done_count % 100 == 0)
            || this.done_count % 1000 == 0) {
                this.output_node.textContent = "Running, "
                    + this.done_count + " complete, "
                    + tests.num_pending + " remain";
            }
        }
    };

    Output.prototype.show_results = function (tests, harness_status)
    {
        if (this.phase >= this.COMPLETE) {
            return;
        }
        if (!this.enabled)
        {
            return;
        }
        if (!this.output_node) {
            this.resolve_log();
        }
        this.phase = this.COMPLETE;

        var log = this.output_node;
        if (!log)
        {
            return;
        }
        var output_document = this.output_document;

        while (log.lastChild)
        {
            log.removeChild(log.lastChild);
        }

        if (script_prefix != null) {
            var stylesheet = output_document.createElementNS(xhtml_ns, "link");
            stylesheet.setAttribute("rel", "stylesheet");
            stylesheet.setAttribute("href", script_prefix + "testharness.css");
            var heads = output_document.getElementsByTagName("head");
            if (heads.length) {
                heads[0].appendChild(stylesheet);
            }
        }

        var status_text = {};
        status_text[Test.prototype.PASS] = "Pass";
        status_text[Test.prototype.FAIL] = "Fail";
        status_text[Test.prototype.TIMEOUT] = "Timeout";
        status_text[Test.prototype.NOTRUN] = "Not Run";

        var status_number = {};
        forEach(tests, function(test) {
                    var status = status_text[test.status];
                    if (status_number.hasOwnProperty(status))
                    {
                        status_number[status] += 1;
                    } else {
                        status_number[status] = 1;
                    }
                });

        function status_class(status)
        {
            return status.replace(/\s/g, '').toLowerCase();
        }

        var summary_template = ["section", {"id":"summary"},
                                ["h2", {}, "Summary"],
                                ["p", {}, "Found ${num_tests} tests"],
                                function(vars) {
                                    var rv = [["div", {}]];
                                    var i=0;
                                    while (status_text.hasOwnProperty(i)) {
                                        if (status_number.hasOwnProperty(status_text[i])) {
                                            var status = status_text[i];
                                            rv[0].push(["div", {"class":status_class(status)},
                                                        ["label", {},
                                                         ["input", {type:"checkbox", checked:"checked"}],
                                                         status_number[status] + " " + status]]);
                                        }
                                        i++;
                                    }
                                    return rv;
                                }];

        log.appendChild(render(summary_template, {num_tests:tests.length}, output_document));

        forEach(output_document.querySelectorAll("section#summary label"),
                function(element)
                {
                    on_event(element, "click",
                             function(e)
                             {
                                 if (output_document.getElementById("results") === null)
                                 {
                                     e.preventDefault();
                                     return;
                                 }
                                 var result_class = element.parentNode.getAttribute("class");
                                 var style_element = output_document.querySelector("style#hide-" + result_class);
                                 var input_element = element.querySelector("input");
                                 if (!style_element && !input_element.checked) {
                                     style_element = output_document.createElementNS(xhtml_ns, "style");
                                     style_element.id = "hide-" + result_class;
                                     style_element.textContent = "table#results > tbody > tr."+result_class+"{display:none}";
                                     output_document.body.appendChild(style_element);
                                 } else if (style_element && input_element.checked) {
                                     style_element.parentNode.removeChild(style_element);
                                 }
                             });
                });

        // This use of innerHTML plus manual escaping is not recommended in
        // general, but is necessary here for performance.  Using textContent
        // on each individual <td> adds tens of seconds of execution time for
        // large test suites (tens of thousands of tests).
        function escape_html(s)
        {
            return s.replace(/\&/g, "&amp;")
                .replace(/</g, "&lt;")
                .replace(/"/g, "&quot;")
                .replace(/'/g, "&#39;");
        }

        function has_assertions()
        {
            for (var i = 0; i < tests.length; i++) {
                if (tests[i].properties.hasOwnProperty("assert")) {
                    return true;
                }
            }
            return false;
        }
        
        function get_assertion(test)
        {
            if (test.properties.hasOwnProperty("assert")) {
                if (Array.isArray(test.properties.assert)) {
                    return test.properties.assert.join(' ');
                }
                return test.properties.assert;
            }
            return '';
        }
        
        log.appendChild(document.createElementNS(xhtml_ns, "section"));
        var assertions = has_assertions();
        var html = "<h2>Details</h2><table id='results' " + (assertions ? "class='assertions'" : "" ) + ">"
            + "<thead><tr><th>Result</th><th>Test Name</th>"
            + (assertions ? "<th>Assertion</th>" : "")
            + "<th>Message</th></tr></thead>"
            + "<tbody>";
        for (var i = 0; i < tests.length; i++) {
            html += '<tr class="'
                + escape_html(status_class(status_text[tests[i].status]))
                + '"><td>'
                + escape_html(status_text[tests[i].status])
                + "</td><td>"
                + escape_html(tests[i].name)
                + "</td><td>"
                + (assertions ? escape_html(get_assertion(tests[i])) + "</td><td>" : "")
                + escape_html(tests[i].message ? tests[i].message : " ")
                + "</td></tr>";
        }
        html += "</tbody></table>";
        try {
            log.lastChild.innerHTML = html;
        } catch (e) {
            log.appendChild(document.createElementNS(xhtml_ns, "p"))
               .textContent = "Setting innerHTML for the log threw an exception.";
            log.appendChild(document.createElementNS(xhtml_ns, "pre"))
               .textContent = html;
        }
    };

    var output = new Output();
    add_start_callback(function (properties) {output.init(properties);});
    add_result_callback(function (test) {output.show_status(tests);});
    add_completion_callback(function (tests, harness_status) {output.show_results(tests, harness_status);});

    /*
     * Template code
     *
     * A template is just a javascript structure. An element is represented as:
     *
     * [tag_name, {attr_name:attr_value}, child1, child2]
     *
     * the children can either be strings (which act like text nodes), other templates or
     * functions (see below)
     *
     * A text node is represented as
     *
     * ["{text}", value]
     *
     * String values have a simple substitution syntax; ${foo} represents a variable foo.
     *
     * It is possible to embed logic in templates by using a function in a place where a
     * node would usually go. The function must either return part of a template or null.
     *
     * In cases where a set of nodes are required as output rather than a single node
     * with children it is possible to just use a list
     * [node1, node2, node3]
     *
     * Usage:
     *
     * render(template, substitutions) - take a template and an object mapping
     * variable names to parameters and return either a DOM node or a list of DOM nodes
     *
     * substitute(template, substitutions) - take a template and variable mapping object,
     * make the variable substitutions and return the substituted template
     *
     */

    function is_single_node(template)
    {
        return typeof template[0] === "string";
    }

    function substitute(template, substitutions)
    {
        if (typeof template === "function") {
            var replacement = template(substitutions);
            if (replacement)
            {
                var rv = substitute(replacement, substitutions);
                return rv;
            }
            else
            {
                return null;
            }
        }
        else if (is_single_node(template))
        {
            return substitute_single(template, substitutions);
        }
        else
        {
            return filter(map(template, function(x) {
                                  return substitute(x, substitutions);
                              }), function(x) {return x !== null;});
        }
    }

    function substitute_single(template, substitutions)
    {
        var substitution_re = /\${([^ }]*)}/g;

        function do_substitution(input) {
            var components = input.split(substitution_re);
            var rv = [];
            for (var i=0; i<components.length; i+=2)
            {
                rv.push(components[i]);
                if (components[i+1])
                {
                    rv.push(String(substitutions[components[i+1]]));
                }
            }
            return rv;
        }

        var rv = [];
        rv.push(do_substitution(String(template[0])).join(""));

        if (template[0] === "{text}") {
            substitute_children(template.slice(1), rv);
        } else {
            substitute_attrs(template[1], rv);
            substitute_children(template.slice(2), rv);
        }

        function substitute_attrs(attrs, rv)
        {
            rv[1] = {};
            for (var name in template[1])
            {
                if (attrs.hasOwnProperty(name))
                {
                    var new_name = do_substitution(name).join("");
                    var new_value = do_substitution(attrs[name]).join("");
                    rv[1][new_name] = new_value;
                };
            }
        }

        function substitute_children(children, rv)
        {
            for (var i=0; i<children.length; i++)
            {
                if (children[i] instanceof Object) {
                    var replacement = substitute(children[i], substitutions);
                    if (replacement !== null)
                    {
                        if (is_single_node(replacement))
                        {
                            rv.push(replacement);
                        }
                        else
                        {
                            extend(rv, replacement);
                        }
                    }
                }
                else
                {
                    extend(rv, do_substitution(String(children[i])));
                }
            }
            return rv;
        }

        return rv;
    }

 function make_dom_single(template, doc)
 {
     var output_document = doc || document;
     if (template[0] === "{text}")
     {
         var element = output_document.createTextNode("");
         for (var i=1; i<template.length; i++)
         {
             element.data += template[i];
         }
     }
     else
     {
         var element = output_document.createElementNS(xhtml_ns, template[0]);
         for (var name in template[1]) {
             if (template[1].hasOwnProperty(name))
             {
                 element.setAttribute(name, template[1][name]);
             }
         }
         for (var i=2; i<template.length; i++)
         {
             if (template[i] instanceof Object)
             {
                 var sub_element = make_dom(template[i]);
                 element.appendChild(sub_element);
             }
             else
             {
                 var text_node = output_document.createTextNode(template[i]);
                 element.appendChild(text_node);
             }
         }
     }

     return element;
 }


 function make_dom(template, substitutions, output_document)
    {
        if (is_single_node(template))
        {
            return make_dom_single(template, output_document);
        }
        else
        {
            return map(template, function(x) {
                           return make_dom_single(x, output_document);
                       });
        }
    }

 function render(template, substitutions, output_document)
    {
        return make_dom(substitute(template, substitutions), output_document);
    }

    /*
     * Utility funcions
     */
    function assert(expected_true, function_name, description, error, substitutions)
    {
        if (expected_true !== true)
        {
            throw new AssertionError(make_message(function_name, description,
                                                  error, substitutions));
        }
    }

    function AssertionError(message)
    {
        this.message = message;
    }

    function make_message(function_name, description, error, substitutions)
    {
        for (var p in substitutions) {
            if (substitutions.hasOwnProperty(p)) {
                substitutions[p] = format_value(substitutions[p]);
            }
        }
        var node_form = substitute(["{text}", "${function_name}: ${description}" + error],
                                   merge({function_name:function_name,
                                          description:(description?description + " ":"")},
                                          substitutions));
        return node_form.slice(1).join("");
    }

    function filter(array, callable, thisObj) {
        var rv = [];
        for (var i=0; i<array.length; i++)
        {
            if (array.hasOwnProperty(i))
            {
                var pass = callable.call(thisObj, array[i], i, array);
                if (pass) {
                    rv.push(array[i]);
                }
            }
        }
        return rv;
    }

    function map(array, callable, thisObj)
    {
        var rv = [];
        rv.length = array.length;
        for (var i=0; i<array.length; i++)
        {
            if (array.hasOwnProperty(i))
            {
                rv[i] = callable.call(thisObj, array[i], i, array);
            }
        }
        return rv;
    }

    function extend(array, items)
    {
        Array.prototype.push.apply(array, items);
    }

    function forEach (array, callback, thisObj)
    {
        for (var i=0; i<array.length; i++)
        {
            if (array.hasOwnProperty(i))
            {
                callback.call(thisObj, array[i], i, array);
            }
        }
    }

    function merge(a,b)
    {
        var rv = {};
        var p;
        for (p in a)
        {
            rv[p] = a[p];
        }
        for (p in b) {
            rv[p] = b[p];
        }
        return rv;
    }

    function expose(object, name)
    {
        var components = name.split(".");
        var target = window;
        for (var i=0; i<components.length - 1; i++)
        {
            if (!(components[i] in target))
            {
                target[components[i]] = {};
            }
            target = target[components[i]];
        }
        target[components[components.length - 1]] = object;
    }

    function forEach_windows(callback) {
        // Iterate of the the windows [self ... top, opener]. The callback is passed
        // two objects, the first one is the windows object itself, the second one
        // is a boolean indicating whether or not its on the same origin as the
        // current window.
        var cache = forEach_windows.result_cache;
        if (!cache) {
            cache = [[self, true]];
            var w = self;
            var i = 0;
            var so;
            var origins = location.ancestorOrigins;
            while (w != w.parent)
            {
                w = w.parent;
                // In WebKit, calls to parent windows' properties that aren't on the same
                // origin cause an error message to be displayed in the error console but
                // don't throw an exception. This is a deviation from the current HTML5
                // spec. See: https://bugs.webkit.org/show_bug.cgi?id=43504
                // The problem with WebKit's behavior is that it pollutes the error console
                // with error messages that can't be caught.
                //
                // This issue can be mitigated by relying on the (for now) proprietary
                // `location.ancestorOrigins` property which returns an ordered list of
                // the origins of enclosing windows. See:
                // http://trac.webkit.org/changeset/113945.
                if(origins) {
                    so = (location.origin == origins[i]);
                }
                else
                {
                    so = is_same_origin(w);
                }
                cache.push([w, so]);
                i++;
            }
            w = window.opener;
            if(w)
            {
                // window.opener isn't included in the `location.ancestorOrigins` prop.
                // We'll just have to deal with a simple check and an error msg on WebKit
                // browsers in this case.
                cache.push([w, is_same_origin(w)]);
            }
            forEach_windows.result_cache = cache;
        }

        forEach(cache,
                function(a)
                {
                    callback.apply(null, a);
                });
    }

    function is_same_origin(w) {
        try {
            'random_prop' in w;
            return true;
        } catch(e) {
            return false;
        }
    }

    function supports_post_message(w)
    {
        var supports;
        var type;
        // Given IE  implements postMessage across nested iframes but not across
        // windows or tabs, you can't infer cross-origin communication from the presence
        // of postMessage on the current window object only.
        //
        // Touching the postMessage prop on a window can throw if the window is
        // not from the same origin AND post message is not supported in that
        // browser. So just doing an existence test here won't do, you also need
        // to wrap it in a try..cacth block.
        try
        {
            type = typeof w.postMessage;
            if (type === "function")
            {
                supports = true;
            }
            // IE8 supports postMessage, but implements it as a host object which
            // returns "object" as its `typeof`.
            else if (type === "object")
            {
                supports = true;
            }
            // This is the case where postMessage isn't supported AND accessing a
            // window property across origins does NOT throw (e.g. old Safari browser).
            else
            {
                supports = false;
            }
        }
        catch(e) {
            // This is the case where postMessage isn't supported AND accessing a
            // window property across origins throws (e.g. old Firefox browser).
            supports = false;
        }
        return supports;
    }
})();
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