563487 - removeEventListener fails when called before addEventListener

Status: RESOLVED FIXED

(Core :: DOM: Events, defect)

Description

[James Schend]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.0.19) Gecko/2010031422 Firefox/3.0.19 ( .NET CLR 3.5.30729)
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729)

A call to removeEventListener during page load throws an exception if made before a call to addEventListener on the same object.

Reproducible: Always

Steps to Reproduce:
1. Write a Javascript that attempts to use removeEventListener before a cooresponding addEventListener
2. Add exception handling around the removeEventListener call
3. Load the page (see referenced URL)
Actual Results:  
Firefox returns the following exception:

[Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMEventTarget.removeEventListener]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: http://schend.net/pages/removeEventHandler_bug.html ::  :: line 18" data: no]

Expected Results:  
No exception

The specification (URL below) says nothing about requiring that addEventListener be called first. Therefore, I believe this is a bug in Firefox.

http://www.w3.org/2003/01/dom2-javadoc/org/w3c/dom/events/EventTarget.html#removeEventListener_java.lang.String__org.w3c.dom.events.EventListener__boolean_

Workaround:
When not certain whether addEventListener has been called before or not, wrap calls to removeEventListener in a try/catch block.

Comment 1

[Gubment Cheez]

doesn't give an answer either way, so I would assume it's up to the implementor to deal with it how they see fit.

Comment 2

[Gubment Cheez]

cancel previous comment, I'm a dumbass
<Remco> <censored>: From the spec: "Calling removeEventListener with arguments which do not identify any currently registered EventListener on the EventTarget has no effect."
<Remco> So it shouldn't throw an exception

Comment 3

[Boris Zbarsky [:bzbarsky]]

Attachment: Fix

James, thank you very much for the clear bug report and the testcase!

Comment 4

[Boris Zbarsky [:bzbarsky]]

Pushed http://hg.mozilla.org/mozilla-central/rev/782230094d98