Optimize _.pairs.

Former-commit-id: 1de87609a8635fb8d48bc558fbdabc545da53b4b

README.md

@@ -209,7 +209,6 @@ require({
  * `_.defer`
  * `_.difference`
  * `_.each`
- * `_.escape`
  * `_.every`, `_.all`
  * `_.extend`
  * `_.filter`, `_.select`
@@ -220,6 +219,7 @@ require({
  * `_.groupBy`
  * `_.indexOf`
  * `_.intersection`
+ * `_.invert`
  * `_.invoke`
  * `_.isArguments`
  * `_.isDate`
@@ -238,6 +238,7 @@ require({
  * `_.min`
  * `_.mixin`
  * `_.omit`
+ * `_.pairs`
  * `_.pick`
  * `_.pluck`
  * `_.reduce`, `_.foldl`, `_.inject`

build.js

@@ -595,7 +595,7 @@
       .replace(/(?: *\/\/.*\n)*\s*'( *)<% *if *\(isKeysFast[\s\S]+?'\1<% *} *else *\{ *%>.+\n([\s\S]+?) *'\1<% *} *%>.+/, '$2')
       // remove `isKeysFast` from `beforeLoop.object` of `mapIteratorOptions`
       .replace(/=\s*'\s*\+\s*\(isKeysFast.+/, "= []'")
-      // remove `isKeysFast` from `inLoop.object` of `mapIteratorOptions`, `invoke`, `pluck`, and `sortBy`
+      // remove `isKeysFast` from `inLoop.object` of `mapIteratorOptions`, `invoke`, `pairs`, `pluck`, and `sortBy`
       .replace(/'\s*\+\s*\(isKeysFast[^)]+?\)\s*\+\s*'/g, '.push')
       // remove data object property assignment in `createIterator`
       .replace(/\s*.+?\.isKeysFast *=.+/, '');

lodash.js

@@ -1865,7 +1865,7 @@
    * @static
    * @memberOf _
    * @category Objects
-   * @param {Object} object The object to inspect..
+   * @param {Object} object The object to inspect.
    * @returns {Array} Returns new array of key-value pairs.
    * @example
    *
@@ -1875,7 +1875,7 @@
   var pairs = createIterator({
     'args': 'object',
     'init':'[]',
-    'inLoop': 'result.push([index, value])'
+    'inLoop': 'result'  + (isKeysFast ? '[ownIndex] = ' : '.push') + '([index, value])'
   });
 
   /**

perf/perf.js

@@ -864,6 +864,18 @@
 
   /*--------------------------------------------------------------------------*/
 
+  suites.push(
+    Benchmark.Suite('`_.invert`')
+      .add('Lo-Dash', '\
+        lodash.invert(object)'
+      )
+      .add('Underscore', '\
+        _.invert(object)'
+      )
+  );
+
+  /*--------------------------------------------------------------------------*/
+
   suites.push(
     Benchmark.Suite('`_.invoke` iterating an array')
       .add('Lo-Dash', '\
@@ -1104,6 +1116,18 @@
 
   /*--------------------------------------------------------------------------*/
 
+  suites.push(
+    Benchmark.Suite('`_.pairs`')
+      .add('Lo-Dash', '\
+        lodash.pairs(object)'
+      )
+      .add('Underscore', '\
+        _.pairs(object)'
+      )
+  );
+
+  /*--------------------------------------------------------------------------*/
+
   suites.push(
     Benchmark.Suite('`_.pick`')
       .add('Lo-Dash', '\