0.0.2 • Public • Published

Shadow Styles

Build Status

WebComponents bring Shadow DOM with isolated CSS to some browsers. This script simulates CSS isolation for all modern browsers (IE9+, Firefox...).


CommonJS applications may need to include the mutation-observer polyfill NPM package as well if they need to support browsers that don't suppport MutationObserver natively:

npm install mutation-observer shadowstyles

Or downoad the built file and manually add tag:

<script src="build/shadowStyles.min.js"></script>


Pass one argument: array, string, or element. String provides a selector to match new shadow root elements. Element provides a direct reference to a root element. Array can contain a combination of both.

// Example with selector string only
// Example with array containing both types
  'x-foo', // All x-foo elements will have shadow styled children
  document.getElementById('something') // Specific element

Targeting simulated shadows

Shadowed elements are given a shadow attribute that must be present in the selector:

shadowed-element[shadow] p { color: blue; }

Detecting native support

When using in conjunction with the Platform.js Shadow DOM polyfill, it can be useful to know whether the shadow DOM is emulated. Check the boolean constant:


Note: I'm considering wrapping the polyfilled createShadowRoot() to automatically isolate the shadow CSS, also allowing createShadowRoot(false) to skip style isolation. See test/mockup/webcomponent.html for implementation details.

How it works

  1. Search for child DOM of elements to isolate.
  2. Find which rules apply to those elements and add a :not(buffer-attr*="uniqueId") pseudo-class with a unique ID to each rule. Shadowed elements gain the buffer attribute containing the unique ID of each negated rule.

Why not ::shadow?

Originally, the plan of this project was to support styles using the native ::shadow pseudo-class syntax. Until the fifteenth commit, this worked, but only if all the page's stylesheets were rewritten completely. By only using selectors that the browser already supports, the script can skip parsing all of your CSS itself and rely on the browser's interpretation, only making small changes as needed. The final result is much smoother operation.

Still to do

  • Handle nested shadow DOM correctly

Build / Run Tests

# Clone repository to current directory 
$ git clone
cd shadowstyles
$ npm install
# Install Grunt Client 
$ npm install -g grunt-cli
# Run default operation to build minified file 
$ grunt
# Running tests locally requires Selenium jar in repo 
# For example, 2.45.0: 
$ wget
# If not running 2.45.0, update filename in GruntFile.js 
# Test using grunt-nightwatch: 
$ grunt nightwatch:local
# Or use default test command alias: 
$ npm test




npm i shadowstyles

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  • numtel