1446212 - Suggestion: document (or link) the return value for 'listener' in addEventListener.

Status: RESOLVED FIXED

(Developer Documentation Graveyard :: General, enhancement, P1)

Description

[Benoit Girard (:BenWa)]

:: Developer Documentation Request

      Request Type: Correction
     Gecko Version: unspecified
 Technical Contact: 

:: Details

This is the first result for a search for `addeventlistener callback return value` but the value is not documented. The EventListener link doesn't document it. This information is likely in bugzilla but I think it could be made easier to find. It's a pretty important part of the web platform.

Comment 1

[Eric Shepherd [:sheppy]]

As far as I'm able to gather, there is no return value for addEventListener()'s callback. I can find nothing in the spec or in any other document I've looked at that says there is one. If that's incorrect, guidance would be appreciated.

Obviously, either way, this needs clarification. I just want to clarify it correctly. :)

Comment 2

[Benoit Girard (:BenWa)]

Attachment: test

I'm having trouble finding a good source:
https://stackoverflow.com/questions/23333466/what-is-the-different-return-false-and-event-preventdefault-in-javascript

I've been testing and checking against the Firefox source and the value is ignored. It's unclear if this was ever a thing or not. Looks like maybe I got confused by a non-standard polyfill.

Maybe we want to close this out or explicitly document this as being void. I'm unsure if further code archeology would yield something or not. The spec idl confirm that this is now void.

Comment 3

[Benoit Girard (:BenWa)]

Here's a better source:
https://stackoverflow.com/questions/1357118/event-preventdefault-vs-return-false

jQuery treats return false as both preventDefault and stopPropogation and is the source of the confusion here. DOM0 treats return false as preventDefault but DOM2 (addEventListener) does not. So its safe to document this as void.

Comment 4

[Eric Shepherd [:sheppy]]

To clarify this, I've cleaned up the addEventListener() pagea little, adding among other things a section about the callback: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#The_event_listener_callback