Some javascript debug helpers for Tampermonkey

tamperdebug.js

// ==UserScript==
// @name         Sven's awesome debug collection
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  debug the stuff
// @include      *
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    console.log("Press F8 when the console is open to trigger 'debugger'");
    console.log("use breakOn(obj, 'propertyName') to break on changes of the property of obj.");
    console.log("other example: breakOn(obj, 'propertyName', null, (val) => { console.log(val); return val > 400; }) to break on changes of the property of obj if new value > 400.");
    function KeyCheck(e) {
        // Key code 24 is 'F8'
        if(e.keyCode === 24) {
            debugger;
        }
    }
    window.addEventListener('keydown', KeyCheck, false);

    window.breakOn = function(obj, propertyName, mode, func) {
        // this is directly from https://github.com/paulmillr/es6-shim
        function getPropertyDescriptor(obj, name) {
            var property = Object.getOwnPropertyDescriptor(obj, name);
            var proto = Object.getPrototypeOf(obj);
            while (property === undefined && proto !== null) {
                property = Object.getOwnPropertyDescriptor(proto, name);
                proto = Object.getPrototypeOf(proto);
            }
            return property;
        }

        function verifyNotWritable() {
            if (mode !== 'read')
                throw "This property is not writable, so only possible mode is 'read'.";
        }

        var enabled = true;
        var originalProperty = getPropertyDescriptor(obj, propertyName);
        var newProperty = { enumerable: originalProperty.enumerable };

        // write
        if (originalProperty.set) {// accessor property
            newProperty.set = function(val) {
                if(enabled && (!func || func && func(val)))
                    debugger;

                originalProperty.set.call(this, val);
            }
        } else if (originalProperty.writable) {// value property
            newProperty.set = function(val) {
                if(enabled && (!func || func && func(val)))
                    debugger;

                originalProperty.value = val;
            }
        } else  {
            verifyNotWritable();
        }

        // read
        newProperty.get = function(val) {
            if(enabled && mode === 'read' && (!func || func && func(val)))
                debugger;

            return originalProperty.get ? originalProperty.get.call(this, val) : originalProperty.value;
        }

        Object.defineProperty(obj, propertyName, newProperty);

        return {
            disable: function() {
                enabled = false;
            },

            enable: function() {
                enabled = true;
            }
        };
    };
})();