434678 - A position fixed node's offsetParent should return null

Status: NEW

(Core :: DOM: CSS Object Model, defect)

Description

[Gérard Talbot]

CSSOM View Module, offsetParent attribute states that 

"
If any of the following holds true return null and terminate this algorithm:
(...)
    The element’s computed value of the position property is fixed.
"
https://www.w3.org/TR/cssom-view/#dom-htmlelement-offsetparent

Steps to reproduce:
1- Load provided URL
2- Click the [return document.getElementById("PositionFixedElem").offsetParent] button

Actual results in Firefox 2.0.0.14 rv: 1.8.1.14 build 20080404 and in Firefox 3.0 RC1 rv: 1.9 build 2008051206 under XP Pro SP3:
document.getElementById("PositionFixedElem").offsetParent = [object HTMLBodyElement]

Expected results:
document.getElementById("PositionFixedElem").offsetParent = null

Internet Explorer 7, Internet Explorer 8 beta 1 and Opera 9.50 will return null.

Component set to DOM: CSSOM : please change it if that's wrong.
I have searched for a duplicate and did not find one. 
I have not checked the testcase with a trunk nightly build: so version 1.9.0 for now.

Comment 1

[Gérard Talbot]

I also get the actual results with Seamonkey 2.0a1pre rv:1.9 build 2008051902.
So, changing version to Trunk

Comment 2

[Gérard Talbot]

bug 255754 comment#12

Comment 3

[Jaroslav Zaruba]

Obviously this also means that there is currently no way to compute actual offset (position) of an elment with position:fixed.

offsetTop:
"If the offsetParent of element A is null or the HTML body element return the distance, as number of CSS pixels, between the top border edge of element A and the canvas origin and stop this algorithm."

Currently the offsetTop property of position:fixed element always contains 0.

Comment 4

[Gérard Talbot]

Last time I checked, Safari 3.1.1 and IE 8 passed this test.

Now, Chrome 25.0.1364.172, Konqueror 4.10.1 and Opera 12.14 passes this test.

Firefox 19.0.2 fails this test.

Confirming

Comment 5

[Gérard Talbot]

"
If any of the following holds true return null and terminate this algorithm:
(...)
    The element’s computed value of the position property is fixed.
"
https://www.w3.org/TR/cssom-view/#dom-htmlelement-offsetparent

now written at
7. Extensions to the HTMLElement Interface
https://www.w3.org/TR/cssom-view/#extensions-to-the-htmlelement-interface

Comment 6

[Gérard Talbot]

I have slightly edited the test to meet the current version of the spec.

CSSOM View Module
W3C Working Draft, 17 March 2016
7. Extensions to the HTMLElement Interface
https://www.w3.org/TR/cssom-view-1/#dom-htmlelement-offsetparent

- - - - - - - - 

(In reply to Jaroslav Zaruba from comment #3)

> Obviously this also means that there is currently no way to compute actual
> offset (position) of an elment with position:fixed.

Correct.

> offsetTop:
> "If the offsetParent of element A is null or the HTML body element return
> the distance, as number of CSS pixels, between the top border edge of
> element A and the canvas origin and stop this algorithm."
> 
> Currently the offsetTop property of position:fixed element always contains 0.

In a test page, I am able to get the offsetTop property of a 'position: fixed' element (which is not 0) with Firefox 47 and Chrome 51. But the spec says it should not be possible since offsetParent of a 'position: fixed' element should be null.

Comment 7

[Davide Cavarretta]

I would like to link https://bugs.webkit.org/show_bug.cgi?id=212372
This is the opposite bug in webkit.

Comment 8

[Daniel Holbert [:dholbert]]

Attachment: reduced testcase

We've got a testcase linked in the URL field with steps in comment 0 -- but for convenience/archival, here's a smaller completely automated testcase that simply reports PASS/FAIL via an alert() when loaded.

This happens to be the cause of bug 1970576, which is how I ran across this.

Comment 9

[Gérard Talbot]

Chromium version 137.0.7151.103 passes both tests: Daniel Holbert's reduced test and mine.

---

It must be stated that Firefox 128.11.0 ESR and Chromium 137.0.7151.103 both fail the map test: the offsetParent of nodeA when nodeA is an <area> element within a <map>

If nodeA is an area HTML element which has a map HTML element somewhere in the ancestor chain, then nodeA.offsetParent returns null because the map element does not have an associated CSS layout box.

Someone could create a bug report on this.