[css-typed-om] Describe that StylePropertyMaps are not live objects

[nainar]

[nainar]

@tabatkins

[jyc]

What does this mean? If a CSS declaration or inline style is otherwise modified (say, through JS), does the specified or inline StylePropertyMap update? What happens if we then call StylePropertyMap::append, for example? Do we append to the declaration or inline style based on its current value while appending to the StylePropertyMap's value based on what it was created with? What does the iterator give us for that property?

[jyc]

Found a definition of "live object" here: https://dom.spec.whatwg.org/#concept-collection-live .
Is this the correct definition? If so, and these are not live objects and therefore do not "operate on the actual underlying data, not a snapshot of the data," what is the point of mutable StylePropertyMaps?

[shans]

To clarify, this is saying that StylePropertyMaps won't update based on style changes from other sources:

var map = el.styleMap;
map.get('height') // for argument's sake, CSSSimpleLength(100, 'px')
el.style.height = '200px';
map.get('height') // will still return CSSSimpleLength(100, 'px')

It might actually be reasonably simple to support live maps for specified objects but for computed styles this gets quite expensive, and it seems best to be consistent.

[shans]

feedback from jyc on irc: this should probably be true only for computed maps, not specified maps.

[tabatkins]

Ah, that's probably fine. I was getting a little confused why .set() worked but wasn't live - there's clearly still a communication channel there. (This doesn't really need to be "live", per se, it's just that .get() goes and gets the value off of the element.)

So yeah, the Readonly version is non-live.

[dbaron]

Resolved to be live for specified and for computed style maps.

[shans]

The only map that's left is the inline map. We didn't specifically talk about this during the spetember f2f but it seems it should be live too. OK for me to close this issue as invalid?

[css-meeting-bot]

The CSS Working Group just discussed #149, and agreed to the following resolutions:

RESOLVED: inline style map is also live

The full IRC log of that discussion

<shane> Topic: https://github.com/w3c/css-houdini-drafts/issues/149
<fantasai> shane: We resolved in September of last year tha tthe specified and computed style maps were live
<fantasai> shane: So if you made changes not through typed OM, would see those changes reflected i nthe map
<fantasai> shane: We did not discuss inline style map
<fantasai> shane: I assume that would be live as well, anyone disagree?
<fantasai> dbaron: I consider that one case of the specified style
<fantasai> shane: Same as specified style in the sense that represents specified style, but has different backing model
<fantasai> Rossen: If we're making specified style live, inline is just specified
<fantasai> RESOLVED: inline style map is also live