Ability to disable JavaScript for a browsing context

[OrKoN]

Chrome allows disabling JavaScript for a specific page: https://pptr.dev/api/puppeteer.page.setjavascriptenabled/

Does it make sense to have this functionality in WebDriver BiDi?

[jgraham]

Yes, I think this makes sense. I'm not 100% sure if Gecko can disable it per (top level) navigable, but in any case it would make sense to have a command that either allowed disabling globally or for certain top-level navigables.

[whimboo]

I'm not 100% sure if Gecko can disable it per (top level) navigable

The BrowsingContext webidl has a allowJavascript flag which would exactly allow us to do that on a per top-level browsing context level.

[shs96c]

What should happen when JS is disabled yet a session wants to evaluate some JS? I believe that should still work, but it's best to confirm

[OrKoN]

@shs96c yeah, that should still work: only the scripts coming from the page should not be executed as if JS is not supported.

[juliandescottes]

The BrowsingContext webidl has a allowJavascript flag which would exactly allow us to do that on a per top-level browsing context level.

For info that's what we use for FF DevTools' "Disable JavaScript" feature

[sadym-chromium]

The CDP method is Emulation.setScriptExecutionDisabled.

[css-meeting-bot]

The Browser Testing and Tools Working Group just discussed Ability to disable JavaScript.

The full IRC log of that discussion

<simonstewart> Topic: Ability to disable JavaScript
<simonstewart> github: https://github.com//issues/746
<simonstewart> jgraham: Apparently people want to test without JS enabled. The idea would be to disable JS for a specific top-level traversable, or perhaps navigable (though the former makes more sense than the latter)
<simonstewart> jgraham: Seems to be very easy to implement in Gecko. Is already implemented in CDP.
<simonstewart> jgraham: What should happen if the session wants to evaluate some JS.
<simonstewart> gsnedders: the WebKit answer is that you can't
<simonstewart> jgraham: In gecko, you can execute in a sandbox, but not in content
<gsnedders> s/you can't/you can't I think/
<simonstewart> simonstewart: people will disable JS, and then the next thing they'll do is try to evaluate some JS (either directly or through a library function)
<simonstewart> jgraham: this feature only really makes sense if you can continue to execute other scripts.
<simonstewart> jgraham: without that, every other command you try and execute, everything else would fall apart
<simonstewart> jgraham: allowing scripts in a sandbox would be implementable.
<simonstewart> simonstewart: for interop between selenium and pages under test, people tend to want to operate on the content
<simonstewart> jimevans: the thing about running with JS disabled is that the people who want to run with JS disabled, really don't want JS at all
<simonstewart> jimevans: they want to ensure that the pages under test continue to work without JS at all
<simonstewart> jimevans: you can still do a lot with HTML and CSS, eg. using forms to send data to a backend.
<simonstewart> jgraham: having a command that sets a flag (as shown in the issue) seems like a quick thing to implement. The question about what to do once JS is disabled is a hard one to answer.
<simonstewart> jgraham: implementations may choose to pre-emptively fail the execute script command if JS is disabled, or want to return unsupported command if the browser doesn't support disabling JS

[OrKoN]

Note that Chrome still allows script evaluation via CDP if JS is disabled for the page and clients like Puppeteer expect this (test).