added mocha to dev dependencies

.travis.yml

@@ -0,0 +1,6 @@
+language: node_js
+node_js:
+  - "0.10"
+  - "0.12"
+  - "4.2.1"
+sudo: false

index.js

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+var path = require('path'),
+  fs = require('fs'),
+  f = require('util').format,
+  semver = require('semver');
+
+var exists = fs.existsSync || path.existsSync;
+
+var find_package_json = function(location) {
+  var found = false;
+
+  while(!found) {
+    if (exists(location + '/package.json')) {
+      found = location;
+    } else if (location !== '/') {
+      location = path.dirname(location);
+    } else {
+      return false;
+    }
+  }
+
+  return location;
+}
+
+var require_optional = function(name, options) {
+  options = options || {};
+  options.strict = typeof options.strict == 'boolean' ? options.strict : true;
+
+  // Locate this module's package.json file
+  var location = find_package_json(__dirname);
+  if(!location) {
+    throw new Error('package.json can not be located');
+  }
+
+  // Read the package.json file
+  var object = JSON.parse(fs.readFileSync(f('%s/package.json', location)));
+  // Is the name defined by interal file references
+  var parts = name.split(/\//);
+
+  // Optional dependencies exist
+  if(!object.peerOptionalDependencies) {
+    throw new Error(f('no optional dependency [%s] defined in peerOptionalDependencies in package.json', parts[0]));
+  } else if(object.peerOptionalDependencies && !object.peerOptionalDependencies[parts[0]]) {
+    throw new Error(f('no optional dependency [%s] defined in peerOptionalDependencies in package.json', parts[0]));
+  }
+
+  var expectedVersions = object.peerOptionalDependencies[parts[0]];
+
+  try {
+    // Validate if it's possible to read the module
+    var moduleEntry = require(name);
+
+    // Resolve the location of the module's package.json file
+    var location = find_package_json(require.resolve(name));
+    if(!location) {
+      throw new Error('package.json can not be located');
+    }
+
+    // Read the module file
+    var dependentOnModule = JSON.parse(fs.readFileSync(f('%s/package.json', location)));
+    // Get the version
+    var version = dependentOnModule.version;
+    // Validate if the found module satisfies the version id
+    if(semver.satisfies(version, expectedVersions) == false
+      && options.strict) {
+        var error = new Error(f('optional dependency [%s] found but version [%s] did not satisfy constraint [%s]', parts[0], version, expectedVersions));
+        error.code = 'OPTIONAL_MODULE_NOT_FOUND';
+        throw error;
+    }
+
+    // Satifies the module requirement
+    return moduleEntry;
+  } catch(err) {
+    if(err.code != 'MODULE_NOT_FOUND') {
+      throw err;
+    }
+  }
+}
+
+require_optional.exists = function(name) {
+  try {
+    var m = require_optional(name);
+    if(m === undefined) return false;
+    return true;
+  } catch(err) {
+    return false;
+  }
+}
+
+module.exports = require_optional;

package.json

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+{
+  "name": "require_optional",
+  "version": "1.0.0",
+  "description": "Allows you declare optionalPeerDependencies that can be satisfied by the top level module but ignored if they are not.",
+  "main": "index.js",
+  "scripts": {
+    "test": "mocha"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/christkv/require_optional.git"
+  },
+  "keywords": [
+    "optional",
+    "require",
+    "optionalPeerDependencies"
+  ],
+  "author": "Christian Kvalheim Amor",
+  "license": "Apache-2.0",
+  "bugs": {
+    "url": "https://github.com/christkv/require_optional/issues"
+  },
+  "homepage": "https://github.com/christkv/require_optional",
+  "dependencies": {
+    "semver": "^5.1.0"
+  },
+  "devDependencies": {
+    "mocha": "^2.4.5",
+    "es6-promise": "^3.0.2",
+    "co": "4.6.0",
+    "bson": "0.4.21"
+  },
+  "peerOptionalDependencies": {
+    "co": ">=5.6.0",
+    "es6-promise": "^3.0.2",
+    "es6-promise2": "^4.0.2",
+    "bson": "0.4.21"
+  }
+}

test/require_optional_tests.js

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+var assert = require('assert'),
+  require_optional = require('../');
+
+describe('Require Optional', function() {
+  describe('top level require', function() {
+    it('should correctly require co library', function() {
+      var promise = require_optional('es6-promise');
+      assert.ok(promise);
+    });
+
+    it('should fail to require es6-promise library', function() {
+      try {
+        require_optional('co');
+      } catch(e) {
+        assert.equal('OPTIONAL_MODULE_NOT_FOUND', e.code);
+        return;
+      }
+
+      assert.ok(false);
+    });
+
+    it('should ignore optional library not defined', function() {
+      assert.equal(undefined, require_optional('es6-promise2'));
+    });
+  });
+
+  describe('internal module file require', function() {
+    it('should correctly require co library', function() {
+      var Long = require_optional('bson/lib/bson/long.js');
+      assert.ok(Long);
+    });
+  });
+
+  describe('top level resolve', function() {
+    it('should correctly use exists method', function() {
+      assert.equal(false, require_optional.exists('co'));
+      assert.equal(true, require_optional.exists('es6-promise'));
+      assert.equal(true, require_optional.exists('bson/lib/bson/long.js'));
+      assert.equal(false, require_optional.exists('es6-promise2'));
+    });
+  });
+});