Is there a way to check if a message event listener already exists?

Question

I want to do something like:

if(noMessageEventListenerExists) {
  globalThis.addEventListener('message', async function (data) {})
}

I saw that working for onClick events but then you have to specify the id of the Element you want to check.

Is there a way to do that for 'message' event listeners?

score 1 · Accepted Answer · answered Aug 22 '22 at 16:38

You need to save a reference to the event listener while creating, like this:

if(!globalThis.onmessage) {
   globalThis.onmessage = globalThis.addEventListener('message', async function (data) {})
}

Otherwise its (probably) lost and you can't find the event listener anymore. Some browsers seem to have (had) a getEventListeners() function, but this seems like nothing that you should rely on.

See more here: removeEventListener without knowing the function

Is there a way to check if a message event listener already exists?

1 Answers1