Closes #47. More conforming Function.prototype.bind.

dist/all.js

@@ -2136,7 +2136,8 @@ fabric.util.string = {
 (function() {
   
   var slice = Array.prototype.slice,
-      apply = Function.prototype.apply;
+      apply = Function.prototype.apply,
+      dummy = function() { };
   
   if (!Function.prototype.bind) {
     /**
@@ -2146,12 +2147,23 @@ fabric.util.string = {
      * @param {Any[]} [...] Values to pass to a bound function
      * @return {Function}
      */
-    Function.prototype.bind = function(thisArg) {
-      var fn = this, args = slice.call(arguments, 1);
-      return args.length
-        ? function() { return apply.call(fn, thisArg, args.concat(slice.call(arguments))); }
-        : function() { return apply.call(fn, thisArg, arguments) };
-    };
+     Function.prototype.bind = function(thisArg) {
+       var fn = this, args = slice.call(arguments, 1), bound;
+       if (args.length) {
+         bound = function() { 
+           return apply.call(fn, this instanceof dummy ? this : thisArg, args.concat(slice.call(arguments))); 
+         };
+       }
+       else {
+         bound = function() { 
+           return apply.call(fn, this instanceof dummy ? this : thisArg, arguments);
+         };
+       }
+       dummy.prototype = this.prototype;
+       bound.prototype = new dummy;
+       
+       return bound;
+     };
   }
   
 })();

src/util/lang_function.js

@@ -1,7 +1,8 @@
 (function() {
   
   var slice = Array.prototype.slice,
-      apply = Function.prototype.apply;
+      apply = Function.prototype.apply,
+      dummy = function() { };
   
   if (!Function.prototype.bind) {
     /**
@@ -11,12 +12,23 @@
      * @param {Any[]} [...] Values to pass to a bound function
      * @return {Function}
      */
-    Function.prototype.bind = function(thisArg) {
-      var fn = this, args = slice.call(arguments, 1);
-      return args.length
-        ? function() { return apply.call(fn, thisArg, args.concat(slice.call(arguments))); }
-        : function() { return apply.call(fn, thisArg, arguments) };
-    };
+     Function.prototype.bind = function(thisArg) {
+       var fn = this, args = slice.call(arguments, 1), bound;
+       if (args.length) {
+         bound = function() { 
+           return apply.call(fn, this instanceof dummy ? this : thisArg, args.concat(slice.call(arguments))); 
+         };
+       }
+       else {
+         bound = function() { 
+           return apply.call(fn, this instanceof dummy ? this : thisArg, arguments);
+         };
+       }
+       dummy.prototype = this.prototype;
+       bound.prototype = new dummy;
+       
+       return bound;
+     };
   }
   
 })();

test/unit/util.js

@@ -1,4 +1,4 @@
-(function(){
+(function() {
   
   module('fabric.util');
   
@@ -166,6 +166,21 @@
     bound = fn.bind(obj, 1);
     same([obj, 1, undefined], bound());
     same([obj, 1, 2], bound(2));
+    
+    function Point(x, y) { 
+      this.x = x; 
+      this.y = y;
+    }
+    
+    var obj = { }
+    var YAxisPoint = Point.bind(obj, 0);
+    var axisPoint = new YAxisPoint(5);
+    
+    same(0, axisPoint.x);
+    same(5, axisPoint.y);
+    
+    ok(axisPoint instanceof Point);
+    // ok(axisPoint instanceof YAxisPoint); <-- fails
   });
   
   test('fabric.util.getById', function() {