No getComputedStyleValue on Polymer.Element?

[arthurevans]

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

[kevinpschaaf]

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

[kevinpschaaf]

This issue was moved to webcomponents/shadycss#83

[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.

@arthurevans 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');
}

[ThomasSchellenbergNextCentury]

@kevinpschaaf In your example, what is el? Is it supposed to be this?

Also, should the documentation be updated with your example? It's currently showing the old incarnation: https://www.polymer-project.org/2.0/docs/devguide/custom-css-properties#style-api

[arthurevans]

@ThomasSchellenbergNextCentury Oops. Yep, we corrected that in the upgrade guide, but missed that example. I've opened a PR to fix that now, thanks!

el in this case is the element you want to get the style from. It doesn't have to be this, of course. The original example was written that way because it was replacing the getComputedStyleValue method on Polymer 1.x elements.