Inject JS code as early as possible

[jonmol]

I'd like to run some javascript before any other scripts are being run on a page and I can't figure out how to do that in a stable sense. What I've tried doing is

• Before calling page.Navigate do page.Eval, but that's of course replaced when the navigation happens so that doesn't work
• Hijack the requests and at the first append my JS to the HTML, similar to "Example_hijack_requests", but that means the JS is outside the closing html tag and it doesn't seems to work.
• Waiting for proto.PageLoadEventFired, but that seems to fire when the page can be considered done, not when the first HTML has been loaded and parsed

I've figured out two possible (but very fragile and hacky) ways to half solve it:

• Hijack the requests and Eval my script on the second request, that won't work on pages not fetching anything apart from the main document.
• Hijack and use a regexp and instead of append insert a script tag inside the head (similar to Example_hijack_requests). That assumes there is a head tag, and feels very fragile (what if it's not HTML, has a very weird layout or a lot of extra properties making the regexp suboptimal)

So, long story short: Is there any event I can use or a cleaner way to do what I'm trying to achieve here?

[ysmood]

Have you checked:

rod/page.go

Lines 878 to 879 in b6b42d8

	// EvalOnNewDocument Evaluates given script in every frame upon creation (before loading frame's scripts).
	func (p *Page) EvalOnNewDocument(js string) (remove func() error, err error) {

Its unit test is its doc:

rod/page_eval_test.go

Lines 14 to 30 in 945ca02

	func TestPageEvalOnNewDocument(t *testing.T) {
	g := setup(t)
	p := g.newPage()
	p.MustEvalOnNewDocument(`window.rod = 'ok'`)
	// to activate the script
	p.MustNavigate(g.blank())
	g.Eq(p.MustEval("() => rod").String(), "ok")
	g.Panic(func() {
	g.mc.stubErr(1, proto.PageAddScriptToEvaluateOnNewDocument{})
	p.MustEvalOnNewDocument(`1`)
	})
	}

[jonmol]

Thanks for the quick answer!

I had indeed missed that function, sorry about that.