Implement getComputedStyle() for font-family (#3614)

[danon]

This is my first PR to jsdom.

I tried to follow example in a8b03af. @domenic let me know if I did it correctly?

[domenic]

It looks like this needs to be set to something like "serif". Can you do that, and then update the test? https://jsbin.com/tulemoreka/edit?html,output

[domenic]

This doesn't appear correct. Per spec it's

list, each item a string and/or keywords

The appropriate test to add is something like

<div style="font-family: serif,sans-serif,     'Times New Roman',Arial"></div>

and then testing that the computed style is serif, sans-serif, "Times New Roman", Arial (with the right quotes and spacing).

Making that work correctly would involve introducing some new infrastructure, probably around here?

jsdom/lib/jsdom/living/helpers/style-rules.js

Lines 214 to 237 in 907daec

	function getComputedValue(element, property) {
	const { computedValue, initial } = exports.propertiesWithResolvedValueImplemented[property];
	if (computedValue === "as-specified") {
	return getSpecifiedValue(element, property);
	} else if (computedValue === "computed-color") {
	const specifiedValue = getSpecifiedValue(element, property);
	// https://drafts.csswg.org/css-color-4/#resolving-other-colors
	if (specifiedValue === "currentcolor") {
	if (property === "color") {
	if (element.parentElement !== null) {
	return getComputedValue(element.parentElement, "color");
	}
	return initial;
	}
	return getComputedValue(element, "color");
	}
	return getComputedOrUsedColor(specifiedValue);
	}
	throw new TypeError(`Internal error: unrecognized computed value instruction '${computedValue}'`);
	}