No getComputedStyleValue on Polymer.Element?

[kevinpschaaf]

From @arthurevans on March 4, 2017 2:54

I suspect it's used significantly less frequently that updateStyles(), but it seemed kind of funky to me that we had a facade for updateStyles on Polymer.Element, but not for getComputedStyleValue.

Currently documented solution for this is:

if (ShadyCSS) {
  style = ShadyCSS.getComputedStyleValue('--something');
} else {
  style = getComputedStyle(this, '--something');
}

Which hopefully I got right. If not, it's here:

https://github.com/Polymer/docs/blame/master/app/2.0/docs/devguide/custom-css-properties.md#L361

Copied from original issue: Polymer/polymer#4374

[kevinpschaaf]

At one point we discussed patching getComputedStyleValue to make the custom property handling in the shim transparent... @azakus ?

[kevinpschaaf]

The plan of record will be for shadycss to patch window.getComputedStyle() to have the return object's getPropertyValue() to return the correct value for custom properties.

Note the correct incantation is the following (note the native syntax in the else clause is what we would shim to work transparently; the syntax is a bit ugly but that's the native API):

if (window.ShadyCSS) {
  style = ShadyCSS.getComputedStyleValue(el, '--something');
} else {
  style = getComputedStyle(el).getPropertyValue('--something');
}

[jimivdw]

Not sure if I should create a separate issue for this, but it appears that it is also no longer possible to retrieve the value of a CSS mixin using getComputedStyleValue, which was possible before. Is this intended? And is there a different way of retrieving mixin values now?

[dfreedm]

@jimivdw that was never supported, and is actually really hard to do with the ApplyShim, as the original --mixin variable is long gone by the time you would try to get the value for it.

[dfreedm]

Closing this issue. Polymer has getComputedStyleValue on the Polymer 1.x hybrid elements.