miscoded

A colleague just noticed that the otherwise excellent jQuery JS library has an "isFunction" method that relies on decompiling functions to figure out if they really, really are functions. This is not a good idea because decompiling functions is an optional feature of the ES-262 spec. It is slow and requires too many resources for certain low-end platforms, so it is not supported by any of the Opera Mobile versions.

Here's the code, complete with a frustrated comment from John Resig himself:

// This may seem like some crazy code, but trust me when I say that this
// is the only cross-browser way to do this. --John
isFunction: function( fn ) {
	return !!fn && typeof fn != "string" && !fn.nodeName && 
		fn.constructor != Array && /function/i.test( fn + "" );
}

John, I feel your pain and that code clearly took quite some effort and testing across various browsers passing in various types of objects - IE collections allowing ()-reference, anyone? It wouldn't surprise me if Opera is one of the culprits that caused you problems here since we try to support some of IE's weirdness and hence "typeof" sometimes returns 'function' when you'd expect it not to.

So I'm sorry to break it to you, but /function/i.test( fn + "" ) won't do what you think on Opera's mobile versions, causing really-hard-to-track-down bugs.

May I suggest adding the below workaround somewhere?

if( (function(){}).toString().match(/\^[ecmascript/i) ) Function.prototype.toString = function(){return 'function'};

Should be all you need..