Ensure _.callback supports binding built-in methods. [closes #576]

lodash.js

@@ -1355,8 +1355,7 @@
       if (typeof func != 'function') {
         return identity;
       }
-      // exit early for no `thisArg` or already bound by `Function#bind`
-      if (typeof thisArg == 'undefined' || !('prototype' in func)) {
+      if (typeof thisArg == 'undefined') {
         return func;
       }
       var data = func[expando];
@@ -1372,7 +1371,7 @@
           }
           if (!data) {
             // checks if `func` references the `this` keyword and stores the result
-            data = reThis.test(source);
+            data = reThis.test(source) || isNative(func);
             setData(func, data);
           }
         }
@@ -8117,7 +8116,7 @@
       var type = typeof func,
           isFunc = type == 'function';
 
-      if (isFunc && (typeof thisArg == 'undefined' || !('prototype' in func))) {
+      if (isFunc && typeof thisArg == 'undefined') {
         return func;
       }
       if (isFunc || func == null) {

test/test.js

@@ -1741,16 +1741,16 @@
 
   (function() {
     test('should create a callback with a falsey `thisArg`', 1, function() {
-      var values = _.map(falsey, function(value) {
+      var expected = _.map(falsey, function(value) {
         return Object(value == null ? root : value);
       });
 
-      var actual = _.map(values, function(value) {
+      var actual = _.map(falsey, function(value) {
         var callback = _.callback(function() { return this; }, value);
         return callback();
       });
 
-      deepEqual(actual, values);
+      ok(_.isEqual(actual, expected));
     });
 
     test('should return `_.identity` when `func` is nullish', 2, function() {
@@ -1818,15 +1818,18 @@
       deepEqual(callback(2), expected);
     });
 
-    test('should return the function provided if already bound with `Function#bind`', 1, function() {
-      function a() {}
+    test('should support binding built-in methods', 2, function() {
+      var object = { 'a': 1 },
+          callback = _.callback(Object.prototype.hasOwnProperty, object);
 
-      var object = {},
-          bound = a.bind && a.bind(object);
+      strictEqual(callback('a'), true);
 
-      if (bound && !('prototype' in bound)) {
-        var bound = a.bind(object);
-        strictEqual(_.callback(bound, object), bound);
+      var fn = function () {},
+          bound = fn.bind && fn.bind(object);
+
+      if (bound) {
+        callback = _.callback(bound, object);
+        notStrictEqual(callback, bound);
       }
       else {
         skipTest();