CODEWITHSUNDEEP
javascript
Dan Novak
Dan Novak

Reputation: 634

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

The scenario: I'm trying to figure out an existing HTML/JavaScript site with a convoluted API. It adds several properties to the window object. I'd like to enumerate only those properties that are not builtins or defaults (e.g. exclude window.location, window.parent, etc.)

Is there an idiomatic JavaScript way to do this? I'd thought of doing a shallow copy in a blank HTML page, then "subtracting" those properties somehow when enumerating the real one.

Ideally, i'd want a way to dump objects to the console or in a watch as if none of the regular window properties existed, only those added with JavaScript source.

Upvotes: 4

Views: 77

Answers (2)

Gabriele Petrioli
Gabriele Petrioli

Reputation: 196002

Expanding on dystroy's answer, in the case where you cannot execute your code before the api, you can create a new window on the fly to grab 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]);
}

Upvotes: 2

Denys Séguret
Denys Séguret

Reputation: 382160

Here's a detailled version of what I proposed in 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 a fiddle

Note that you may execute the first part at start of the page's header, before the import of external scripts. Here's a sample.

Upvotes: 5

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