CSSStyleDeclaration string properties all have `| null` type declaration.

[sccolbert]

lib.dom.d.ts has recently suffixed all of the properties of CSSStyleDeclaration with | null:
https://github.com/Microsoft/TypeScript/blob/master/lib/lib.dom.d.ts#L1382
6814c1d

For those of us using --strictNullChecks, this is forcing a null assertion (!) every time a property is used, even though according to the spec null will never be returned, only an empty string:
https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-getpropertyvalue

The camel-cased attribute attribute, on getting, must return the result of invoking getPropertyValue() with the argument being the result of running the IDL attribute to CSS property algorithm for camel-cased attribute.

The spec does seem to allow null as an argument for setPropertyValue, so technically this a case where allowing a different type for a getter and setter (#2521) would be required to accurately model a builtin.

But in the absence of that, this particular object treats the empty string the same as null for setting, so I think it would be cleaner to simply remove | null from this definition so that we don't have to needlessly null-assert everywhere CSSStyleDeclaration is used.

[mhegazy]

Since this is strictly not per spec, we would like to get some more user feedback to warrant the change.

[inad9300]

Just as a curiosity, why were the nulls added in the first place? What was the feedback then?

[kitsonk]

The libraries are generated from a WebIDL, with overrides. I believe it is still the WebIDL from Edge, though there was a desire to generate it from the spec.

There is seldom any feedback required to make something more compliant with the spec and in many cases it is automatic as the upstream "authority" gets updated. The generator is available at Microsoft/TSJS-lib-generator, which includes the current version of the spec files it uses.

[inad9300]

It's very interesting to know this, thanks! I didn't know such level of automation was in place. This is then definitely related with the issue I just opened about missing HTML tags.

[HolgerJeromin]

Currently we have mixed string and string | null typings 8-/
https://github.com/Microsoft/TypeScript/blob/master/lib/lib.dom.d.ts#L2749

[ypresto]

Perhaps already fixed around here?:
microsoft/TypeScript-DOM-lib-generator#723

[amakhrov]

Looks like this has landed in TS 3.6.4