glimmer-scoped-css

glimmer-scoped-css is an Ember addon that lets you embed <style> tags in component templates that will be scoped to only apply within those components:

If you have app/components/something.hbs:

<style>
  p {
    color: blue;
  }
</style>

<h1>An h1</h1>

<p>A p.</p>

you get this generated HTML:

<h1 data-scopedcss-58ccb4dfe0-e9125e9996>An h1</h1>

<p data-scopedcss-58ccb4dfe0-e9125e9996>A p.</p>

and this generated CSS:

p[data-scopedcss-58ccb4dfe0-e9125e9996] {
  color: blue;
}

Nested components only have the parent component’s styles on elements with ...attributes. You can see this in action in test-app.

Additional features

The implementation is adapted from a Vue PostCSS plugin. It also supports these pseudo-elements:

:global

If you want to use CSS in your component but want a selector to not be scoped, you can use :global:

:global(.red) {
  color: red;
}

The generated CSS will look like this:

.red {
  color: red;
}

:deep

Using :deep on a selector will attach the scoping attribute to the element selector before it.

.a :deep(.b) {
  color: pink;
}

The generated CSS will look like this:

.a[data-scopedcss-3afb00313e] .b {
  color: pink;
}

:rotating_light: Limitations

This is a pre-1.0 release with several limitations:

• it assumes a Webpack build
• it hardcodes Webpack CSS loaders
  • this works fine when you have the default loaders configured by @embroider/webpack
• the styles are in a style element in index.html, not linked
• there is log noise about source maps like this:

  unexpectedly found "<style>\n  p { color: blue" when slicing source, but expected "data-scopedcss-53259f1da9-58ccb4dfe0"

• An open prettier issue means that if you apply prettier to your handlebars, it will format your CSS in a silly way.

Compatibility

• Ember.js v3.28 or above
• Embroider v3.0.0 or above

Installation

ember install glimmer-scoped-css

1. Include in ember-cli-build.js:

    const { Webpack } = require('@embroider/webpack');
   +const { GlimmerScopedCSSWebpackPlugin } = require('glimmer-scoped-css/webpack');
    return require('@embroider/compat').compatBuild(app, Webpack, {
   +  packagerOptions: {
   +    webpackConfig: {
   +      plugins: [new GlimmerScopedCSSWebpackPlugin()],
   +    },
   +  },
    });

In an Ember application

2. Add an in-repo addon to install the Handlebars preprocessor:

   In package.json:

    "ember": {
      "edition": "octane"
   +},
   +"ember-addon": {
   +  "paths": [
   +    "lib/setup-ast-transforms"
   +  ]
    }

   Add lib/setup-ast-transforms/package.json:

   {
     "name": "setup-ast-transforms",
     "keywords": [
       "ember-addon"
     ],
     "dependencies": {
       "glimmer-scoped-css": "*"
     }
   }

   Add lib/setup-ast-transforms/index.js:

    'use strict';
   
    const { installScopedCSS } = require('glimmer-scoped-css');
   
    module.exports = {
      name: require('./package').name,
      setupPreprocessorRegistry(type, registry) {
        if (type === 'parent') {
          installScopedCSS(registry);
        }
      },
    };

In an Ember addon

2. Install the preprocessor directly in the addon’s index.js:

    'use strict'
   +const { installScopedCSS } = require('glimmer-scoped-css');
   
    module.exports = {
      name: require('./package').name,
      isDevelopingAddon() {
        return true;
      },
   +  setupPreprocessorRegistry(type, registry) {
   +    if (type === 'self') {
   +      installScopedCSS(registry);
   +    }
   +  },
    };

Usage

Add a top-level <style> element in your component .hbs file and it will be scoped to elements in that component only. It also works in <template> in .gjs/.gts files.

Nested <style> elements cannot be processed for scoping. Use <style unscoped> if you need a nested element, it will not receive scoping attributes and will be passed through to output without the unscoped attribute.

Architecture

glimmer-scoped-css consists of two parts. The first part is an AST transform that takes as input your <style> tags inside handlebars and emits as output specially crafted import statements that account for that scoped CSS.

The second part is a plugin for your current environment (by default, webpack) that satisfies the specially-crafted import statements by turning them into CSS. To implement a new plugin, you should use import { isScopedCSSRequest, decodeScopedCSSRequest } from 'glimmer-scoped-css' to identify these imports and turn them back into CSS, respectively.

Troubleshooting

node/no-missing-require lint errors

Error:    6:51  error  "glimmer-scoped-css/webpack" is not found         node/no-missing-require

The eslint-plugin-node package that produces this error doesn’t understand the exports structure supported by newer Node versions and is unmaintained. Ember CLI has moved to using eslint-plugin-n as a drop-in replacement as of 4.10.

Changing to eslint-plugin-n and updating the lint configuration fixes these errors.

Contributing

See the Contributing guide for details.

License

This project is licensed under the MIT License.