How does Page.expose_function work?

[Havunen]

Hi,

Can somebody provide example or more info how Page.expose_function is supposed to be used?

chromiumoxide/src/page.rs

Lines 272 to 290 in 0897fb5

	pub async fn expose_function(
	&self,
	name: impl Into<String>,
	function: impl AsRef<str>,
	) -> Result<()> {
	let name = name.into();
	let expression = utils::evaluation_string(function, &["exposedFun", name.as_str()]);
	self.execute(AddBindingParams::new(name)).await?;
	self.execute(AddScriptToEvaluateOnNewDocumentParams::new(
	expression.clone(),
	))
	.await?;
	// TODO add execution context tracking for frames
	//let frames = self.frames().await?;
	Ok(())
	}

I got it to compile used like this:

        let pages = browser.pages().await.expect("Failed to get pages");
        let page = pages.first().expect("No pages found");

        // Correct usage based on the provided snippet and error description
        let js_function = r#"
    function(args) {
        console.log('SetInterval called with args:', args);
        return Promise.resolve();
    }
"#;

        page.expose_function("$#MT#SetInterval", js_function)
            .await
            .expect("Failed to expose function!");

and it seems to get registered client side:

But that does not fulfill the purpose why expose_function exists, the idea is to expose a method so client side JS could call the Rust backend as shown here: https://pptr.dev/api/puppeteer.page.exposefunction.

Am I missing something here or is this functionality broken?

[Havunen]

rust-headless-chrome's expose_function implementation seems to do more what it is supposed to do:
https://github.com/rust-headless-chrome/rust-headless-chrome/blob/4de5b8efceaeacfc3c432b2d756a67fdc01f70d4/src/browser/tab/mod.rs#L452-L491

https://github.com/rust-headless-chrome/rust-headless-chrome/blob/4de5b8efceaeacfc3c432b2d756a67fdc01f70d4/tests/expose_function.rs#L11

[Havunen]

This does not seem to print anything either...

let (browser, mut handler) = Browser::launch(browser_config)
    .await
    .expect("Failed to launch browser");

// Spawn a task to handle browser events
tokio::spawn(async move {
    while let Some(event) = handler.next().await {
        println!("Event: {:?}", event);
    }
});

page.execute(AddBindingParams::new("MTMTMT1")).await.expect("Failed to add binding");

let mut event_listener: EventStream<EventBindingCalled> = browser.event_listener().await.expect("Failed to get event listener");

tokio::spawn(async move {
    while let Some(event) = event_listener.next().await {
        println!("Event 2: {:?}", event);
    }
});

The MTMTMT1 is shown in the client side side but calling it does not print anything in rust backend

... there has to be some way

[Havunen]

After going through the source code I figured out how this is done. I opened a PR for new example to possibly help others with similar issue. #224

[Havunen]

Achieving this functionality is possible by using let mut listener = page.event_listener::<EventBindingCalled>().await?; Wether expose_function method works as expected is still unclear