Chrome extension - script loaded event?

Question

Is it possible to get an event (or other way of knowing) when a specific script is loaded into a page?

E.g. I have a page action that should perform action if jQuery is present and have finished loading.

Can't you wait for `window.onload` and then look for `window.jQuery`? — Teepeemm, Aug 24 '14 at 22:36
@Teepeemm Not that simple, since a content script won't have `window.jQuery` exposed to it from the page. — Xan, Aug 25 '14 at 21:03

score 0 · Answer 1 · answered Aug 26 '14 at 00:29

I can think of two approaches:

(1) Look to see if a jQuery script was included: in contentScript.js:

if ( document.querySelector('script[src*="jquery"]') ) {
    // probably has jquery
}

(2) Look to see if jQuery is defined: in contentScript.js:

window.addEventListener('jQueryFound',function() {
    // probably has jquery
});
var scriptTag = document.createElement('script');
scriptTag.textContent
   = "if ( window.jQuery ) { window.dispatchEvent(new Event('jQueryFound')); }"
document.head.appendChild(scriptTag);

(1) will fail if the site author is using bad filenames. (2) will fail if they’ve redefined window.jQuery (or if I messed up my javascript events api, since I’m not the best at javascript).

You could also simplify the above by including jQuery as a content script before you detect if jQuery is included. ;)

score 0 · Accepted Answer · answered Aug 30 '14 at 18:00

0

I ended up listening for "DOMContentLoaded" and then perform required actions.

Thanks for all input

answered Aug 30 '14 at 18:00

Martin Nilsson

659
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1

This will tell you when the page has finished loading. But determining whether a specific script is present is a separate and more challenging problem. – Teepeemm Aug 31 '14 at 00:57

score -1 · Answer 3 · edited May 23 '17 at 11:51

-1

There seems to be a similar stack overflow issue here for the web at large that I think will also apply to your extension: Trying to fire the onload event on script tag

It seems that you can set the src and onload elements of a script to get an event when the script loads.

edited May 23 '17 at 11:51

Community

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1

answered Aug 25 '14 at 20:17

petewil-G

99
4

Does not apply. OP tries to detect a ` – Xan Aug 25 '14 at 20:21

Chrome extension - script loaded event?

3 Answers3