(breaking change) moving _.reduce's method signature to that of ECMA5. _.reduce(obj, iterator, memo). Updated tests and docs.

index.html

@@ -216,10 +216,10 @@ var lyrics = [
 _(lyrics).chain()
   .map(function(line) { return line.words.split(' '); })
   .flatten()
-  .reduce({}, function(counts, word) {
+  .reduce(function(counts, word) {
     counts[word] = (counts[word] || 0) + 1;
     return counts;
-}).value();
+}, {}).value();
 
 =&gt; {lumberjack : 2, all : 4, night : 2 ... }</pre>
 
@@ -261,7 +261,7 @@ _.map([1, 2, 3], function(num){ return num * 3 });
 =&gt; [3, 6, 9]</pre>
 
       <p id="reduce">
-        <b class="header">reduce</b><code>_.reduce(list, memo, iterator, [context])</code>
+        <b class="header">reduce</b><code>_.reduce(list, iterator, memo, [context])</code>
         <span class="alias">Aliases: <b>inject, foldl</b></span>
         <br />
         Also known as <b>inject</b> and <b>foldl</b>, <b>reduce</b> boils down a
@@ -270,12 +270,12 @@ _.map([1, 2, 3], function(num){ return num * 3 });
         <b>iterator</b>.
       </p>
       <pre>
-var sum = _.reduce([1, 2, 3], 0, function(memo, num){ return memo + num });
+var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num }, 0);
 =&gt; 6
 </pre>
 
       <p id="reduceRight">
-        <b class="header">reduceRight</b><code>_.reduceRight(list, memo, iterator, [context])</code>
+        <b class="header">reduceRight</b><code>_.reduceRight(list, iterator, memo, [context])</code>
         <span class="alias">Alias: <b>foldr</b></span>
         <br />
         The right-associative version of <b>reduce</b>. Delegates to the
@@ -285,7 +285,7 @@ var sum = _.reduce([1, 2, 3], 0, function(memo, num){ return memo + num });
       </p>
       <pre>
 var list = [[0, 1], [2, 3], [4, 5]];
-var flat = _.reduceRight(list, [], function(a, b) { return a.concat(b); });
+var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
 =&gt; [4, 5, 2, 3, 0, 1]
 </pre>
 

test/chaining.js

@@ -12,11 +12,11 @@ $(document).ready(function() {
     var counts = _(lyrics).chain()
       .map(function(line) { return line.split(''); })
       .flatten()
-      .reduce({}, function(hash, l) {
+      .reduce(function(hash, l) {
         hash[l] = hash[l] || 0;
         hash[l]++;
         return hash;
-    }).value();
+    }, {}).value();
     ok(counts['a'] == 16 && counts['e'] == 10, 'counted all the letters in the song');
   });
 

test/collections.js

@@ -53,22 +53,22 @@ $(document).ready(function() {
   });
 
   test('collections: reduce', function() {
-    var sum = _.reduce([1, 2, 3], 0, function(sum, num){ return sum + num; });
+    var sum = _.reduce([1, 2, 3], function(sum, num){ return sum + num; }, 0);
     equals(sum, 6, 'can sum up an array');
 
     var context = {multiplier : 3};
-    sum = _.reduce([1, 2, 3], 0, function(sum, num){ return sum + num * this.multiplier; }, context);
+    sum = _.reduce([1, 2, 3], function(sum, num){ return sum + num * this.multiplier; }, 0, context);
     equals(sum, 18, 'can reduce with a context object');
 
-    sum = _.inject([1, 2, 3], 0, function(sum, num){ return sum + num; });
+    sum = _.inject([1, 2, 3], function(sum, num){ return sum + num; }, 0);
     equals(sum, 6, 'aliased as "inject"');
 
-    sum = _([1, 2, 3]).reduce(0, function(sum, num){ return sum + num; });
+    sum = _([1, 2, 3]).reduce(function(sum, num){ return sum + num; }, 0);
     equals(sum, 6, 'OO-style reduce');
   });
 
   test('collections: reduceRight', function() {
-    var list = _.foldr([1, 2, 3], '', function(memo, num){ return memo + num; });
+    var list = _.foldr([1, 2, 3], function(memo, num){ return memo + num; }, '');
     equals(list, '321', 'can perform right folds');
   });
 

underscore.js

@@ -92,8 +92,11 @@
 
   // Reduce builds up a single result from a list of values, aka inject, or foldl.
   // Delegates to JavaScript 1.8's native reduce if available.
-  _.reduce = function(obj, memo, iterator, context) {
-    if (nativeReduce && obj.reduce === nativeReduce) return obj.reduce(_.bind(iterator, context), memo);
+  _.reduce = function(obj, iterator, memo, context) {
+    if (nativeReduce && obj.reduce === nativeReduce) {
+      if (context) iterator = _.bind(iterator, context);
+      return obj.reduce(iterator, memo);
+    }
     each(obj, function(value, index, list) {
       memo = iterator.call(context, memo, value, index, list);
     });
@@ -102,10 +105,13 @@
 
   // The right-associative version of reduce, also known as foldr. Uses
   // Delegates to JavaScript 1.8's native reduceRight if available.
-  _.reduceRight = function(obj, memo, iterator, context) {
-    if (nativeReduceRight && obj.reduceRight === nativeReduceRight) return obj.reduceRight(_.bind(iterator, context), memo);
+  _.reduceRight = function(obj, iterator, memo, context) {
+    if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
+      if (context) iterator = _.bind(iterator, context);
+      return obj.reduceRight(iterator, memo);
+    }
     var reversed = _.clone(_.toArray(obj)).reverse();
-    return _.reduce(reversed, memo, iterator, context);
+    return _.reduce(reversed, iterator, memo, context);
   };
 
   // Return the first value which passes a truth test.
@@ -277,11 +283,11 @@
 
   // Return a completely flattened version of an array.
   _.flatten = function(array) {
-    return _.reduce(array, [], function(memo, value) {
+    return _.reduce(array, function(memo, value) {
       if (_.isArray(value)) return memo.concat(_.flatten(value));
       memo.push(value);
       return memo;
-    });
+    }, []);
   };
 
   // Return a version of the array that does not contain the specified value(s).
@@ -293,10 +299,10 @@
   // Produce a duplicate-free version of the array. If the array has already
   // been sorted, you have the option of using a faster algorithm.
   _.uniq = function(array, isSorted) {
-    return _.reduce(array, [], function(memo, el, i) {
+    return _.reduce(array, function(memo, el, i) {
       if (0 == i || (isSorted === true ? _.last(memo) != el : !_.include(memo, el))) memo.push(el);
       return memo;
-    });
+    }, []);
   };
 
   // Produce an array that contains every item shared between all the