371711 - Assigning into the HTMLCollection returned by document.getElementsByTagName should throw

Status: RESOLVED WORKSFORME

(Core :: DOM: Core & HTML, enhancement)

Description

[Jesse Ruderman]

Attachment: testcase

I think the following code should cause an exception to be thrown:

  document.getElementsByTagName('button')[0] = 'wtf';

I don't think this would break web sites, since it crashed for a while (bug 367589) and I was the first to notice.

Comment 1

[Jesse Ruderman]

Strangely, Safari and Opera have the same behavior: it doesn't throw.

Comment 2

[Jesse Ruderman]

WebIDL + DOM Core probably mandates one behavior or another here.

Comment 3

[Cameron McCormack (:heycam)]

Until DOM Core NodeLists are rewritten in Web IDL (probably as part of Web DOM Core) no particular behaviour is mandated at the moment.  But if it were, I think the behaviour should be not to throw, unless in strict mode.  (Because the "0" property that would exist due to the index getter would be [[Writable]]:false.)

Comment 4

[:Ms2ger (he/him; ⌚ UTC+1/+2)]

Attachment: Strict mode test case

AFAICT from WebIDL, the assignments in this test should throw, but nobody does that. Cameron, could you have a look?

Comment 5

[Cameron McCormack (:heycam)]

Yes, with that test, the first assignment should throw a TypeError (the [[DefineOwnProperty]] algorithm in http://dev.w3.org/2006/webapi/WebIDL/#defineownproperty says to Reject (= throw when in strict mode) if the object supports indexed properties but doesn't have a setter or creator defined on the interface.

The two last w() calls should then write out "[object HTMLButtonElement]" and "undefined".

Note that this is a slightly different case from throwing due to being in strict mode and assigning to a property that exists and is a currently supported property index (*mouthful*).  If everyone just ignores the assignment, I'm open to changing the spec to require that instead of throwing, if people think it's a good idea.  I think it's more consistent with the aims of strict mode to throw in this case, though.

Comment 6

[Boris Zbarsky [:bzbarsky]]

Worksforme in strict mode, as expected.