browser.runtime.onMessage.addListener only accepts 2 arguments

[eugbyte]

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onMessage

The actual browser.runtime.onMessage.addListener accepts 3 arguments:, message, sender, sendResponse. However, the current implementation only accepts 2 arguments: message, sender

[eugbyte]

created pull request here:
#55

[brnbs]

Please merge this ASAP

[Lusito]

As you can see in the page you linked: "Returning a Promise is now preferred, as sendResponse() will be removed from the W3C spec."

Please use a promise as return value instead of using sendResponse.

I'm going to keep this open, as this pops up regularly, as people don't seem to search before opening new tickets: #53, #46, #45, #31, #7

[brnbs]

I landed here from Chrome Developer website where I found no mention about returning a Promise, however I gave it a try and just wanted to confirm that this works the same as calling sendResponse:

browser.runtime.onMessage.addListener((message: string) => {
    if (message == "whatever") {
        // Do something
        return Promise.resolve("response");
    }
});

[Lusito]

Chrome documentation is not about the W3C standard. They don't care about the standard at all. If you try to target multiple browsers, I suggest you use the MDN documentation. Of course, there will be things you need to check if you want chrome-only features and for that you'll need to use the chrome documentation.

[linonetwo]

This makes it not easy to pass Observable from backgroundScript to contentScript, an Observable need to send multiple times, after subscribe.

I need something like

    const ovserver = {
      next: (value) => sender.send(subscriptionId, { type: ResponseType.Next, value }),
      error: (error: Error) => sender.send(subscriptionId, { type: ResponseType.Error, error: Errio.stringify(error) }),
      complete: () => sender.send(subscriptionId, { type: ResponseType.Complete }),
    };

To achieve something like https://github.com/frankwallis/electron-ipc-proxy

[fregante]

@linonetwo That's not how sendResponse works.

If you call sendReponse multiple times, all calls past the first one will just be ignored. There's no such sender.send function.

sendResponse is defined by its name, it sends a response, not a generic message.

[joshsmith]

As seen in mozilla/webextension-polyfill#386 (comment) sendResponse should now be supported by this package.

See also updated MDN documentation: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onMessage

[lhk]

@Lusito I think the post from joshsmith is important, wouldn't it make sense to update the specification?

[Lusito]

Will be fixed in the next version.

For the record: I don't think it's a good idea, because people easily misunderstand this and think they can call it multiple times.