fix: convert value to DOMString

[cdoublev]

Fix #129.

[codecov-commenter]

Codecov Report

Merging #130 (3b74e06) into master (b527ed7) will increase coverage by 43.13%.
The diff coverage is 94.82%.

@@             Coverage Diff             @@
##           master     #130       +/-   ##
===========================================
+ Coverage   37.39%   80.52%   +43.13%     
===========================================
  Files          87       87               
  Lines        1182     1171       -11     
  Branches      227      216       -11     
===========================================
+ Hits          442      943      +501     
+ Misses        633      180      -453     
+ Partials      107       48       -59     

Impacted Files	Coverage Δ
lib/properties/borderColor.js	90.90% <ø> (+90.90%)	⬆️
lib/properties/borderWidth.js	78.26% <ø> (+78.26%)	⬆️
lib/parsers.js	82.53% <86.95%> (+1.88%)	⬆️
lib/CSSStyleDeclaration.js	94.64% <100.00%> (+3.46%)	⬆️
lib/properties/backgroundPosition.js	66.66% <100.00%> (+66.66%)	⬆️
lib/properties/borderSpacing.js	38.88% <100.00%> (+38.88%)	⬆️
lib/properties/borderStyle.js	90.90% <100.00%> (+90.90%)	⬆️
lib/properties/clip.js	84.00% <100.00%> (+84.00%)	⬆️
lib/properties/flex.js	85.71% <100.00%> (+85.71%)	⬆️
lib/properties/flexBasis.js	90.90% <100.00%> (+90.90%)	⬆️
... and 87 more

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[cdoublev]

Unfortunately, despite my successive attemps, this PR will not be enough in all cases. Eg. with style.borderStyle = { toString: () => 'solid' }, the setter for border-style will not validate the value.

I feel like this package (and the issue related to this PR) requires a pretty large overhaul. IMO parsers.valueType could be removed, as well as isValid, which are almost always equivalent to parseTypeA(val) ?? parseTypeB(val) ?? ... and parseType(val) !== undefined, respectively, and each implemented property setter could be transformed to convert value to a DOM String before being passed to the custom setter, if any, ie. set: () => transformedSet(toDOMString(val)).

If any of the maintainers think spending more time on this is pointless because of a lack of their time, please let me know!

[cdoublev]

Finally found a way to fix style.borderStyle = { toString: () => 'solid' }.

But one notable change is that implemented properties are no longer parsed and generated with babel. I believe this was only required by cssom in order to be run in a browser. I didn't bother to install jsdom to run its tests with this change.

Why do I need this problem to be fixed?

I maintain a JS library for animating HTML elements. In my jest tests, which depends on cssstyle via jsdom, many different CSS properties have their value evaluated. In summary, I want to make a change that transforms the final statement animated.style.property = stringValue into animated.style.property = { toString: () => stringValue }, but that makes those tests failing.

I can redefine the animated properties descriptors, so that I don't have to wait for a fix to this package and a new version of jsdom and jest:

// setupFile.js

const createSetter = initialSetter => function set(v) {
    return initialSetter.bind(this)(String(v))
}
const descriptor = Object.getOwnPropertyDescriptor(CSSStyleDeclaration.prototype, 'backgroundColor')

// descriptor.set = createSetter(descriptor.set) // Doesn't work
Object.defineProperty(
    CSSStyleDeclaration.prototype,
    'backgroundColor',
    { ...descriptor, set: createSetter(descriptor.set) })

// Repeat for each animated property name used in tests

This library does not have any test setup file at this time. It's better like that and without having to update such file every time a test involving a new CSS property needs to be added.

[cdoublev]

Superseded by #140.