Add option to selectively include style properties when cloning element

[Justineo]

Description

Added a new option includeStyleProperties which allows users to selectively copy computed style.

Motivation and Context

Currently we need to copy and serialize all the style properties in computedStyle for every node. In performance sensitive scenarios we would like to be able to minimize the time consumed when cloning node styles, for example:

• Style attributes that are determined to be unused can be removed
• Removing style attributes that only affect interaction behavior (eg. pointer-events, cursor, etc.)

Apart from performance use cases, as CSS custom properties are not iterable from CSSStyleDeclaration, they are not included in the snapshot image with current implementation (see #433). This new option may also help in this case as it allows users to manually specify custom properties that are used.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Enhancement (changes that improvement of current feature or performance)
• Refactoring (changes that neither fixes a bug nor adds a feature)
• Test Case (changes that add missing tests or correct existing tests)
• Code style optimization (changes that do not affect the meaning of the code)
• Docs (changes that only update documentation)
• Chore (changes that don't modify src or test files)

Self Check before Merge

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[vivcat]

👋 @Justineo

💖 Thanks for opening this pull request! 💖

Please follow the contributing guidelines. And we use semantic commit messages to streamline the release process.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add graph.scale() method
• docs: graph.getShortestPath is now available

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We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[codecov]

Codecov Report

Patch coverage: 61.53% and no project coverage change.

Comparison is base (b751cbf) 62.93% compared to head (f9efd26) 62.93%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #436   +/-   ##
=======================================
  Coverage   62.93%   62.93%           
=======================================
  Files          10       10           
  Lines         580      580           
  Branches      143      143           
=======================================
  Hits          365      365           
  Misses        151      151           
  Partials       64       64           

Files Changed	Coverage Δ
src/apply-style.ts	100.00% <ø> (ø)
src/clone-pseudos.ts	29.16% <50.00%> (ø)
src/clone-node.ts	71.42% <54.54%> (ø)
src/util.ts	62.80% <77.77%> (ø)

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[aeharding]

@Justineo FWIW I was inspired by your PR and made a PR to modern-screenshot with this :)

[hcampos-professional]

Instead of allocating a new array with all the property names for each node in order call .forEach on it, it would be even faster to just use a good-old for loop to iterate over all the properties. Since CSSStyleDeclaration is "array-like", it works well:

const propertyNames = options.includeStyleProperties ?? sourceStyle;
for (let i = 0; i < propertyNames; ++i) {
  const name = propertyNames[i];
  let value = sourceStyle.getPropertyValue(name);
  // ...
}