Underscore 1.0.4, with _.memoize

Author: jashkenas

index.html

@@ -108,18 +108,16 @@ <h1>Underscore.js</h1>
 
     <h2>Downloads <i style="padding-left: 12px; font-size:12px;">(Right-click, and use "Save As")</i></h2>
 
-    <p>
-      <table>
-        <tr>
-          <td><a href="underscore.js">Development Version (1.0.3)</a></td>
-          <td><i>24kb, Uncompressed with Comments</i></td>
-        </tr>
-        <tr>
-          <td><a href="underscore-min.js">Production Version (1.0.3)</a></td>
-          <td><i>2.9kb, Packed and Gzipped</i></td>
-        </tr>
-      </table>
-    </p>
+    <table>
+      <tr>
+        <td><a href="underscore.js">Development Version (1.0.4)</a></td>
+        <td><i>24kb, Uncompressed with Comments</i></td>
+      </tr>
+      <tr>
+        <td><a href="underscore-min.js">Production Version (1.0.4)</a></td>
+        <td><i>2.9kb, Packed and Gzipped</i></td>
+      </tr>
+    </table>
 
     <h2>Table of Contents</h2>
 
@@ -144,15 +142,16 @@ <h2>Table of Contents</h2>
       <br />
       <span class="methods"><a href="#first">first</a>, <a href="#rest">rest</a>, <a href="#last">last</a>,
       <a href="#compact">compact</a>, <a href="#flatten">flatten</a>, <a href="#without">without</a>, <a href="#uniq">uniq</a>,
-      <a href="#intersect">intersect</a>, <a href="#zip">zip</a>, <a href="#indexOf">indexOf</a></span>,
+      <a href="#intersect">intersect</a>, <a href="#zip">zip</a>, <a href="#indexOf">indexOf</a>,
       <a href="#lastIndexOf">lastIndexOf</a>, <a href="#range">range</a></span>
     </p>
 
     <p>
       <b>Functions</b>
       <br />
-      <span class="methods"><a href="#bind">bind</a>, <a href="#bindAll">bindAll</a>, <a href="#delay">delay</a>,
-      <a href="#defer">defer</a>, <a href="#wrap">wrap</a></span>, <a href="#compose">compose</a></span>
+      <span class="methods"><a href="#bind">bind</a>, <a href="#bindAll">bindAll</a>, 
+      <a href="#memoize">memoize</a>, <a href="#delay">delay</a>, <a href="#defer">defer</a>, 
+      <a href="#wrap">wrap</a>, <a href="#compose">compose</a></span>
     </p>
 
     <p>
@@ -173,7 +172,7 @@ <h2>Table of Contents</h2>
       <br />
       <span class="methods"><a href="#noConflict">noConflict</a>,
       <a href="#identity">identity</a>, <a href="#times">times</a>, 
-      <a href="#breakLoop">breakLoop</a></span>, <a href="#mixin">mixin</a></span>, 
+      <a href="#breakLoop">breakLoop</a>, <a href="#mixin">mixin</a>, 
       <a href="#uniqueId">uniqueId</a>, <a href="#template">template</a></span>
     </p>
 
@@ -652,6 +651,21 @@ <h2>Function (uh, ahem) Functions</h2>
 _.bindAll(buttonView);
 jQuery('#underscore_button').bind('click', buttonView.onClick);
 =&gt; When the button is clicked, this.label will have the correct value...
+</pre>
+
+      <p id="memoize">
+        <b class="header">memoize</b><code>_.memoize(function, [hashFunction])</code>
+        <br />
+        Memoizes a given <b>function</b> by caching the computed result. Useful
+        for speeding up slow-running computations. If passed an optional 
+        <b>hashFunction</b>, it will be used to compute the hash key for storing
+        the result, based on the arguments to the original function.
+      </p>
+      <pre>
+var fibonacci = function(n) {
+  return n &lt; 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
+};
+var fastFibonacci = _.memoize(fibonacci);
 </pre>
 
       <p id="delay">
@@ -1136,6 +1150,12 @@ <h2>Links &amp; Suggested Reading</h2>
 
       <h2>Change Log</h2>
 
+      <p>
+        <b class="header">1.0.4</b><br />
+        Andri Möll contributed the <tt>_.memoize</tt> function, which can be
+        used to speed up expensive repeated computations by caching the results.
+      </p>
+      
       <p>
         <b class="header">1.0.3</b><br />
         Patch that makes <tt>_.isEqual</tt> return <tt>false</tt> if any property

package.json

@@ -8,5 +8,5 @@
   "dependencies"  : [],
   "lib"           : ".",
   "main"          : "underscore.js",
-  "version"       : "1.0.3"
+  "version"       : "1.0.4"
 }

test/functions.js

@@ -45,6 +45,15 @@ $(document).ready(function() {
     equals(curly.sayHi(), 'hi: moe', 'calling bindAll with no arguments binds all functions to the object');
   });
 
+  test("functions: memoize", function() {
+    var fib = function(n) {
+      return n < 2 ? n : fib(n - 1) + fib(n - 2);
+    };
+    var fastFib = _.memoize(fib);
+    equals(fib(10), 55, 'a memoized version of fibonacci produces identical results');
+    equals(fastFib(10), 55, 'a memoized version of fibonacci produces identical results');
+  });
+
   asyncTest("functions: delay", function() {
     var delayed = false;
     _.delay(function(){ delayed = true; }, 100);

test/objects.js

@@ -16,7 +16,7 @@ $(document).ready(function() {
     "flatten", "foldl", "foldr", "forEach", "functions", "head", "identity", "include",
     "indexOf", "inject", "intersect", "invoke", "isArguments", "isArray", "isBoolean", "isDate", "isElement", "isEmpty", "isEqual",
     "isFunction", "isNaN", "isNull", "isNumber", "isRegExp", "isString", "isUndefined", "keys", "last", "lastIndexOf", "map", "max",
-    "methods", "min", "mixin", "noConflict", "pluck", "range", "reduce", "reduceRight", "reject", "rest", "select",
+    "memoize", "methods", "min", "mixin", "noConflict", "pluck", "range", "reduce", "reduceRight", "reject", "rest", "select",
     "size", "some", "sortBy", "sortedIndex", "tail", "tap", "template", "times", "toArray", "uniq",
     "uniqueId", "values", "without", "wrap", "zip"];
     same(expected, _.methods(_), 'provides a sorted list of functions');

underscore-min.js

@@ -55,7 +55,7 @@
   root._ = _;
 
   // Current version.
-  _.VERSION = '1.0.3';
+  _.VERSION = '1.0.4';
 
   // ------------------------ Collection Functions: ---------------------------
 
@@ -375,6 +375,16 @@
     return obj;
   };
 
+  // Memoize an expensive function by storing its results.
+  _.memoize = function(func, hasher) {
+    var memo = {};
+    hasher = hasher || _.identity;
+    return function() {
+      var key = hasher.apply(this, arguments);
+      return key in memo ? memo[key] : (memo[key] = func.apply(this, arguments));
+    };
+  };
+
   // Delays a function for the given number of milliseconds, and then calls
   // it with the arguments supplied.
   _.delay = function(func, wait) {