Before Angular 2, the Angular team demonstrated what’s possible with Custom Elements. Now, in Angular 4 and above, we can take advantage of the native Custom Element API to transform our Angular Components into truly encapsulated, self-sufficient custom elements. In this tutorial, you’ll learn how to turn an Angular Component into a self-contained Custom Element that can be used anywhere on the web.
What are custom elements
Custom elements are a web standard that allows you to create new HTML tags and extend existing ones. This is useful for creating reusable components that can be used in multiple places. An Angular component can be easily converted into a custom element using the custom Elements API provided by browsers. To do this, we need to register the component with the browser as a custom element which has to be done on the page where it is declared, just before it’s inserted onto the page.
Getting started with a component library in Angular
A component library is a great way to organize your code and keep your components consistent. Plus, it makes it easy to reuse components in other projects. Here’s how to get started with a component library in Angular A) Add ng-metadata to any controller, directive or pipe that should be available as a custom element
- B) Define the custom element in an index.ts file
- C) Set up browser targeting rules
- D) Install dependencies via npm install –save -D @angular/elements (requires TypeScript 2.2 or higher)
The two parts of implementing custom elements in Angular
Creating the wrapper element and polyfill
In order to transform an Angular component into a custom element, you need to create a wrapper element that will act as the host for the Angular component. The next step is to create a polyfill for any browser that doesn’t support custom elements. Once you’ve created the wrapper and polyfill, you can then register the element with Angular. Finally, you can use the custom element in your HTML template.
Creating the native Shadow DOM polyfill
The first step is to create the Shadow DOM polyfill. This will allow us to use the Shadow DOM API in browsers that don’t support it natively. We’ll create a file called shadow-polyfill.js and include it in our HTML file with a script tag. To run this code, we need to import polyfill from ‘./shadow-polyfill’; so, we’ll do this at the top of our script block:
One problem with using Shadow DOM is that CSS styles defined inside the Shadow DOM are not visible outside of it by default. However, there’s a way around this!
Writing a custom renderer in TypeScript
In this post, we’ll show you how to write a custom renderer for an Angular component and turn it into a native custom element. This is useful if you want to use Angular components in other frameworks or if you want to take advantage of the benefits of custom elements.
Creating the host instance and DOM bindings
In order to transform an Angular component into a custom element, we need to create the host instance and DOM bindings. The host instance is responsible for creating the component and its DOM elements, and the DOM bindings are responsible for connecting the component to the DOM. To do this, we first need to create a custom element class that extends HTMLElement. Next, we need to create a factory function that will create an instance of our custom element class. Finally, we need to register our custom element with the browser.
The final step – making it work across browsers