sendResponse undefined when executing browser.runtime.onMessage.addListener((message, sender, sendResponse)

[ghost]

Am I missing something here? According to the docs (https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/runtime/onMessage), onMessage should always have a third 'sendResponse' function parameter. The code around https://github.com/mozilla/webextension-polyfill/blob/master/src/browser-polyfill.js#L330 suggests that I need to define the listener as following:

browser.runtime.onMessage.addListener((message, sender) => {
    return new Promise((resolve, reject) => {

    })
})

Doesn't this break for browsers without the polyfill? (e.g. Firefox/Edge)

[LilDevil]

@jvanveen, I think the part you're missing is in the docs, where it says

To send an asynchronous response, there are two options:

• return true from the event listener. This keeps the sendResponse function valid after the listener returns, so you can call it later.
• return a Promise from the event listener, and resolve when you have the response (or reject it in case of an error).

The code you posted is the 2nd option. This works just fine in Firefox, as well as in Chrome with the polyfill.

If you want a more synchronous version:

browser.runtime.onMessage.addListener((message, sender) => {
  return Promise.resolve("reply");
})

But you are correct that the callback version (sendResponse in the Mozilla docs) does not polyfill correctly.

[LilDevil]

This appears to be a duplicate of #16 where there is lots of interesting discussion of the issue.

[Rob--W]

Closing. This was fixed by #97 and will be released in the next version (0.3.0, see #88).