Javascript property_exists : Class/Object Information : PHP functions in JavaScript JAVASCRIPT TUTORIALS

function property_exists (cls, prop) {
    // Checks if the object or class has a property  
    // 
    // version: 812.3015
    // discuss at: http://phpjs.org/functions/property_exists
    // +   original by: Brett Zamir
    // *     example 1: function class_a() {this.prop1 = 'one'};
    // *     example 1: var instance_a = new class_a();
    // *     example 1: property_exists(instance_a, 'prop1');
    // *     returns 1: true
    // *     example 2: function class_a() {this.prop1 = 'one'};
    // *     example 2: var instance_a = new class_a();
    // *     example 2: property_exists(instance_a, 'prop2');
    // *     returns 2: false
    cls = (typeof cls === 'string') ? window[cls] : cls;
    
    if (typeof cls === 'function' && cls.toSource &&
        cls.toSource().match(new RegExp('this\\.'+prop+'\\s'))
    ) {
        // Hackish and non-standard but can probably detect if setting
        // the property (we don't want to test by instantiating as that
        // may have side-effects)
        return true;
    }

    return (cls[prop] !== undefined && typeof cls[prop] !== 'function')
        || (cls.prototype !== undefined && cls.prototype[prop] !== undefined && typeof cls.prototype[prop] !== 'function')
        || (cls.constructor && cls.constructor[prop] !== undefined && typeof cls.constructor[prop] !== 'function');
}