javascript - how to run greasemonkey script before the page content is displayed?

Question

I am writing a plug-in for Firefox and using greasemonkey script to do that (I compile the user script using this tool http://arantius.com/misc/greasemonkey/script-compiler).

The issue is that the script is run after the page is fully loaded. Meaning the user would see the viewed page in its original form and then the script will apply the changes that I made. My question is there a way to run the user script before the contents of the page is displayed to the user, so the user would only the final version of the website?

Answer 1

EDIT: This post was created prior to the implementation of the @run-at key in Greasemonkey - as noted by Blaise, from Greasemonkey 0.9.8 you may now have the script executed as soon as the page begins to load.

@run-at document-start is described in the wiki as follows:

Start is new as of version 0.9.8. The script will run before any document begins loading, thus before any scripts run or images load.

Note that this means having the script run (potentially) prior to the creation of the DOM and may lead to some inconsistent/unusual behaviour. You will need (a little) more than just this one-line drop-in.

There are a few more details over at the Greasemonkey Wiki: http://wiki.greasespot.net/Metadata_Block#.40run-at

Side-note: The information I have to hand is specifically related to Greasemonkey in the browser. I am unsure whether @run-at document-start works well with the script compiler - I suggest living dangerously.. Test it and find out! ;]

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It is not currently possible to run a user script before the page loads.

To stop the flicker using current versions of Greasemonkey, you could try adding a user-style to your Firefox profile (which is then undone using the script) as described at the Greasemonkey wiki but this would also require each of your users to do the same to benefit from this.

It is something that has been desired for a long time and looking through issue #1103 on Greasemonkey's Github site, a working prototype appears to have been made (but there is no timescale for this to be added to a release version afaik).