This Ember.js addon helps load the js file(s) on demand, i.e. lazy loading, inside the <script> tag in the document <body> using the service m-js-loader .
Ember@^3.0.0
The ambitious SPAs need more than one JS resources (external libraries) and some of these JS resources can be more functionality centric and may not be required to get loaded on the initial screen or may be required only for few of screens. The loading of scripts that are not necessary for the initial page load can be deferred until after the initial load. Doing so can help reduce resource contention and improve performance.
Suppose a web app uses Maps Library (like leaflet) for displaying maps, which comes with its own JS. The maps are displayed only on couple of routes other than home screen. So the home screen is not needed to load the JS for maps. The maps JS should be loaded when the routes displaying maps are requested. In this scenario, its always preferable to load the JS dynamically.
The method to load a JS file on demand.
attr is a JSON object which holds the attribute values for the <script> tag to load JS. It should at least have src property set to the source of the JS.
mJsLoader: Ember.inject.service('m-js-loader'),
beforeModel() {
this.get('mJsLoader').load({
src: 'http://cdn-assets/maps.js',
integrity: 'sha384-shfssiufhnof7348f738f7bw8g+Pmsjshdinwe98',
crossorigin: 'anonymous'
});
}
The service m-js-loader returns a promise. The service listens to the events onload and onerror on the <script> tag in which the JS 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 JS gets loaded then the service can be used inside the beforeModel hook.
mJsLoader: Ember.inject.service('m-js-loader'),
beforeModel() {
return this.get('mJsLoader').load({
src: '/assets/maps.js'
});
}
The service m-js-loader caches the srcs loaded to avoid injecting the same JS more than once.
The service inserts a <script> tag which as good as having it hardcoded at the time of html load. So no CORS issue.
ember install ember-m-js-loader
[Longer description of how to use the addon in apps.]
git clone <repository-url>cd ember-m-js-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.