This Ember.js addon helps load the css file(s) on demand, i.e. lazy loading, inside the <link> tag in the document <head> using the service m-css-loader .
Ember@^3.0.0
CSS are render blocking resources. The ambitious SPAs need more than one CSS resources (external libraries) and some of these CSS resources can be more functionality centric and may not be required to get loaded on the Home screen or may be required only for few of screens.
Suppose a web app uses Maps Library (like leaflet) for displaying maps, which comes with its own CSS. The maps are displayed only on couple of routes other than home screen. So the home screen is not needed to load the CSS for maps. The maps CSS should be loaded when the routes displaying maps are requested. In this scenario, its always preferable to load the CSS dynamically.
The method to load a CSS file on demand.
attr is a JSON object which holds the attribute values for the <link> tag to load CSS. It should at least have href property set to the source of the CSS.
mCssLoader: Ember.inject.service('m-css-loader'),
beforeModel() {
this.get('mCssLoader').load({
href: 'http://cdn-assets/maps.css',
integrity: 'sha384-shfssiufhnof7348f738f7bw8g+Pmsjshdinwe98',
crossorigin: 'anonymous'
});
}
The service m-css-loader returns a promise. The service listens to the events onload and onerror on the <link> tag in which the CSS is loaded. It resolves the promise inside onload event and rejects it if onerror event is raised.
Use of this promise is completely optional and upto the requirement of the app. If a route needs to wait until the CSS gets loaded then the service can be used inside the beforeModel hook.
mCssLoader: Ember.inject.service('m-css-loader'),
beforeModel() {
return this.get('mCssLoader').load({
href: '/assets/maps.css'
});
}
The service m-css-loader caches the hrefs loaded to avoid injecting the same CSS more than once.
The service inserts a <link> tag which as good as having it hardcoded at the time of html load. So no CORS issue.
ember install ember-m-css-loader
[Longer description of how to use the addon in apps.]
git clone <repository-url>cd ember-m-css-loadernpm install
npm run lint:jsnpm run lint:js -- --fix
ember test– Runs the test suite on the current Ember versionember test --server– Runs the test suite in "watch mode"npm test– Runsember try:eachto test your addon against multiple Ember versions
ember serve- Visit the dummy application at http://localhost:4200.
For more information on using ember-cli, visit https://ember-cli.com/.
This project is licensed under the MIT License.