JsPHP: a JavaScript library providing the PHP API

function class_exists (cls) {
    // http://jsphp.co/jsphp/fn/view/class_exists
    // +   original by: Brett Zamir (http://brett-zamir.me)
    // *     example 1: function class_a() {this.meth1 = function () {return true;}};
    // *     example 1: var instance_a = new class_a();
    // *     example 1: class_exists('class_a');
    // *     returns 1: true
    var i = '';
    cls = this.window[cls]; // Note: will prevent inner classes
    if (typeof cls !== 'function') {
        return false;
    }

    for (i in cls.prototype) {
        return true;
    }
    for (i in cls) { // If static members exist, then consider a "class"
        if (i !== 'prototype') {
            return true;
        }
    }
    if (cls.toSource && cls.toSource().match(/this\./)) {
        // Hackish and non-standard but can probably detect if setting
        // a property (we don't want to test by instantiating as that
        // may have side-effects)
        return true;
    }

    return false;
}