user.watch.js

/*
* user.watch v1.0: Cross-browser user.watch
* From http://code.eligrey.com/object.watch/
*
* By Elijah Grey, http://eligrey.com
* Tweaked by Trevor Lalish-Menagh, http://trevmex.com
*
* A shim that partially implements object.watch and object.unwatch
* in browsers that have accessor support.
*
* Public Domain.
* NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
*/

var User = function () {
    return {
        // user.watch
        "watch": function (prop, handler) {
            var val = this[prop],
            getter = function () {
                return val;
            },
            setter = function (newval) {
                return val = handler.call(this, prop, val, newval);
            };

            if (delete this[prop]) { // can't watch constants
                if (Object.defineProperty) { // ECMAScript 5
                    Object.defineProperty(this, prop, {
                        get: getter,
                        set: setter
                    });
                } else if (Object.prototype.__defineGetter__ && Object.prototype.__defineSetter__) { // legacy
                    User.prototype.__defineGetter__.call(this, prop, getter);
                    User.prototype.__defineSetter__.call(this, prop, setter);
                }
            }
        },

        // user.unwatch
        "unwatch": function (prop) {
            var val = this[prop];
            
            delete this[prop]; // remove accessors
            this[prop] = val;
        }
    };
};