Add a message to TypeError from _.bind

Author: mattrobenolt

test/functions.js

@@ -38,6 +38,12 @@
     equal(newBoundf.hello, undefined, 'function should not be bound to the context, to comply with ECMAScript 5');
     equal(Boundf().hello, 'moe curly', "When called without the new operator, it's OK to be bound to the context");
     ok(newBoundf instanceof F, 'a bound instance is an instance of the original function');
+
+    raises(
+      function() { _.bind('notafunction'); },
+      function(actual) { return actual instanceof TypeError && actual.message !== ''; },
+      'throws an error when binding to a non-function'
+    );
   });
 
   test('partial', function() {

underscore.js

@@ -600,7 +600,7 @@
   _.bind = function(func, context) {
     var args, bound;
     if (nativeBind && func.bind === nativeBind) return nativeBind.apply(func, slice.call(arguments, 1));
-    if (!_.isFunction(func)) throw new TypeError;
+    if (!_.isFunction(func)) throw new TypeError('Bind must be called on a function');
     args = slice.call(arguments, 2);
     return bound = function() {
       if (!(this instanceof bound)) return func.apply(context, args.concat(slice.call(arguments)));