[New] return the native bind when available.

implementation.js

@@ -0,0 +1,48 @@
+var ERROR_MESSAGE = 'Function.prototype.bind called on incompatible ';
+var slice = Array.prototype.slice;
+var toStr = Object.prototype.toString;
+var funcType = '[object Function]';
+
+module.exports = function bind(that) {
+    var target = this;
+    if (typeof target !== 'function' || toStr.call(target) !== funcType) {
+        throw new TypeError(ERROR_MESSAGE + target);
+    }
+    var args = slice.call(arguments, 1);
+
+    var bound;
+    var binder = function () {
+        if (this instanceof bound) {
+            var result = target.apply(
+                this,
+                args.concat(slice.call(arguments))
+            );
+            if (Object(result) === result) {
+                return result;
+            }
+            return this;
+        } else {
+            return target.apply(
+                that,
+                args.concat(slice.call(arguments))
+            );
+        }
+    };
+
+    var boundLength = Math.max(0, target.length - args.length);
+    var boundArgs = [];
+    for (var i = 0; i < boundLength; i++) {
+        boundArgs.push('$' + i);
+    }
+
+    bound = Function('binder', 'return function (' + boundArgs.join(',') + '){ return binder.apply(this,arguments); }')(binder);
+
+    if (target.prototype) {
+        var Empty = function Empty() {};
+        Empty.prototype = target.prototype;
+        bound.prototype = new Empty();
+        Empty.prototype = null;
+    }
+
+    return bound;
+};

index.js

@@ -1,49 +1,3 @@
-var ERROR_MESSAGE = 'Function.prototype.bind called on incompatible ';
-var slice = Array.prototype.slice;
-var toStr = Object.prototype.toString;
-var funcType = '[object Function]';
-
-module.exports = function bind(that) {
-    var target = this;
-    if (typeof target !== 'function' || toStr.call(target) !== funcType) {
-        throw new TypeError(ERROR_MESSAGE + target);
-    }
-    var args = slice.call(arguments, 1);
-
-    var bound;
-    var binder = function () {
-        if (this instanceof bound) {
-            var result = target.apply(
-                this,
-                args.concat(slice.call(arguments))
-            );
-            if (Object(result) === result) {
-                return result;
-            }
-            return this;
-        } else {
-            return target.apply(
-                that,
-                args.concat(slice.call(arguments))
-            );
-        }
-    };
-
-    var boundLength = Math.max(0, target.length - args.length);
-    var boundArgs = [];
-    for (var i = 0; i < boundLength; i++) {
-        boundArgs.push('$' + i);
-    }
-
-    bound = Function('binder', 'return function (' + boundArgs.join(',') + '){ return binder.apply(this,arguments); }')(binder);
-
-    if (target.prototype) {
-        var Empty = function Empty() {};
-        Empty.prototype = target.prototype;
-        bound.prototype = new Empty();
-        Empty.prototype = null;
-    }
-
-    return bound;
-};
+var implementation = require('./implementation');
 
+module.exports = Function.prototype.bind || implementation;

test/index.js

@@ -1,6 +1,6 @@
 var test = require('tape');
 
-var functionBind = require('../index');
+var functionBind = require('../implementation');
 var getCurrentContext = function () { return this; };
 
 test('functionBind is a function', function (t) {
@@ -9,13 +9,11 @@ test('functionBind is a function', function (t) {
 });
 
 test('non-functions', function (t) {
-    var errorPrefix = 'Function.prototype.bind called on incompatible ';
     var nonFunctions = [true, false, [], {}, 42, 'foo', NaN, /a/g];
-    t.plan(nonFunctions.length * 2);
+    t.plan(nonFunctions.length);
     for (var i = 0; i < nonFunctions.length; ++i) {
         try { functionBind.call(nonFunctions[i]); } catch (ex) {
             t.ok(ex instanceof TypeError, 'throws when given ' + String(nonFunctions[i]));
-            t.equal(ex.message, errorPrefix + String(nonFunctions[i]), 'exception message is correct for ' + nonFunctions[i]);
         }
     }
     t.end();
@@ -250,4 +248,3 @@ test('bound function length', function (t) {
         st.end();
     });
 });
-