Added support for ECMAScript 5 native bind method if available. Add…

…itional unit test to cover multiple argument binds.

test/functions.js

@@ -20,6 +20,10 @@ $(document).ready(function() {
 
     var func = _.bind(func, this, 'curly');
     equals(func(), 'hello: curly', 'the function was completely applied in advance');
+
+    var func = function(salutation, firstname, lastname) { return salutation + ': ' + firstname + ' ' + lastname };
+    func = _.bind(func, this, 'hello', 'moe', 'curly');
+    equals(func(), 'hello: moe curly', 'the function was partially applied in advance and can accept multiple arguments');
   });
 
   test("functions: bindAll", function() {

underscore.js

@@ -21,7 +21,7 @@
   var breaker = {};
 
   // Save bytes in the minified (but not gzipped) version:
-  var ArrayProto = Array.prototype, ObjProto = Object.prototype;
+  var ArrayProto = Array.prototype, ObjProto = Object.prototype, FuncProto = Function.prototype;
 
   // Create quick reference variables for speed access to core prototypes.
   var slice            = ArrayProto.slice,
@@ -42,7 +42,8 @@
     nativeIndexOf      = ArrayProto.indexOf,
     nativeLastIndexOf  = ArrayProto.lastIndexOf,
     nativeIsArray      = Array.isArray,
-    nativeKeys         = Object.keys;
+    nativeKeys         = Object.keys,
+    nativeBind         = FuncProto.bind;
 
   // Create a safe reference to the Underscore object for use below.
   var _ = function(obj) { return new wrapper(obj); };
@@ -408,6 +409,7 @@
   // optionally). Binding with arguments is also known as `curry`.
   _.bind = function(func, obj) {
     var args = slice.call(arguments, 2);
+    if(nativeBind && func.bind === nativeBind) return FuncProto.bind.apply(func, slice.call(arguments, 1));
     return function() {
       return func.apply(obj || {}, args.concat(slice.call(arguments)));
     };