How to list only properties / methods of JavaScript objects added at runtime?

Question

Scenario: I'm trying to figure out an existing HTML / JavaScript site with a confusing API. It adds several properties to the window object. I would like to list only those properties that are not built-in or standard (e.g. exclude window.location , window.parent , etc.)

Is there an idiomatic JavaScript way to do this? I thought about making a shallow copy on an empty HTML page, and then “subtracting” these properties in some way when listing the real one.

Ideally, I need a way to reset objects to the console or to the clock, as if none of the usual window properties existed, only those that were added with the JavaScript source code.

Answer 1

Expanding dystroy's answer , in the case when you cannot execute your code before api, you can create a new window on the fly to capture its properties (since it will be "clean")
(also using hasOwnProperty to exclude inherited properties)

 window.preexistingkeys = []; var w = window.open(); for (var key in w) if(window.hasOwnProperty(key)) window.preexistingkeys.push(key); w.close(); for (var key in window) { if (window.hasOwnProperty(key) && window.preexistingkeys.indexOf(key)==-1) console.log(key, window[key]); } 

Answer 2

Here is a detailed version of what I suggested in the comment:

 window.preexistingkeys = []; for (var key in window) window.preexistingkeys.push(key); // your convoluted api here for (var key in window) { if (window.preexistingkeys.indexOf(key)==-1) console.log(key, window[key]); }​ 

with violin

Note that you can complete the first part at the beginning of the page title before importing external scripts. Here is an example .