can I find when window.onclick() function overridden?

Question

in javascript, is it possible to make an event handler when a function attribute changes from

window.onclick = function() {  ....function 1...... };

to

window.onclick = function() {  ....function 2..... };

Answer 1

This is a few years old, but it has worked great for me. An SO user posted an open-source object watcher a few years back. It modifies the object prototype so that you watch for changes to specific properties of the object.

window.watch('onclick', function() { console.log('changed'); });
window.onclick = function() {  console.log('click1'); };
window.onclick = function() {  console.log('click2'); };

JSFiddle: https://jsfiddle.net/gou48xpa/

Source code: https://gist.github.com/eligrey/384583 (released with MIT license)

if (!Object.prototype.watch) {
    Object.defineProperty(Object.prototype, "watch", {
          enumerable: false
        , configurable: true
        , writable: false
        , value: function (prop, handler) {
            var
              oldval = this[prop]
            , newval = oldval
            , getter = function () {
                return newval;
            }
            , setter = function (val) {
                oldval = newval;
                return newval = handler.call(this, prop, oldval, val);
            }
            ;

            if (delete this[prop]) { // can't watch constants
                Object.defineProperty(this, prop, {
                      get: getter
                    , set: setter
                    , enumerable: true
                    , configurable: true
                });
            }
        }
    });
}

// object.unwatch
if (!Object.prototype.unwatch) {
    Object.defineProperty(Object.prototype, "unwatch", {
          enumerable: false
        , configurable: true
        , writable: false
        , value: function (prop) {
            var val = this[prop];
            delete this[prop]; // remove accessors
            this[prop] = val;
        }
    });
}