Question

If I browse to about:blank, open the script console and type the following:

var x = function() {
    console.info(this.toString() + ' -- ' + arguments.length.toString());
};
x.bind;

The response shows that x.bind is implemented in native code:

function bind() { [native code] }

However, when I pull up the script console on a page of my web app and execute the same statements, it looks like x.bind is not natively impplemented:

function (a){var b=this;return function(){b.apply(a,arguments)}}

What would cause this implementation to switch like this? Is there potentially something I’m setting in my javascript that could cause this? I’m using jQuery on the page – would that have an impact?

Answer 1

Not jQuery, but some other libraries/scripts add bind to Function.prototype, and some of them do it without checking if it’s already there, happily overwriting the native implementation. I assume you must be using some other script (besides jQuery) on the page, and that other script (whether it’s a jQuery plug-in or whatever) is overwriting without checking.

I’ve just tested in Chrome, and regardless of whether I have jQuery loaded or not, from within an actual page looking at a function’s bind property shows the native code marker. (In contrast, if I load the latest Prototype, it overwrites Chrome’s native version with its own.)

Example with page with no libraries, output on Chrome:

Prototype not loaded
jQuery not loaded
function bind() { [native code] }

Example with page with latest jQuery, output on Chrome:

Prototype not loaded
jQuery found: 1.6.2
function bind() { [native code] }

Example with page with latest Prototype, output on Chrome:

Prototype found: 1.7
jQuery not loaded
function bind(context) { if (arguments.length < 2 && Object.isUndefined(arguments[0])) return this; var __method = this, args = slice.call(arguments, 1); return function() { var a = merge(args, arguments); return __method.apply(context, a); } }

From your example, you’re not loading the latest Prototype, but something is overwriting Function.prototype.bind.