The mapping rules between Angular components and custom elements are crucial for transforming Angular components into custom elements, which are reusable web components that can be used in any HTML document or web application. Here’s a detailed explanation of these mapping rules:
Component Inputs to Custom Element Attributes:
Angular's @Input() properties in components are mapped to attributes in the custom element. This allows data to be passed to the custom element through HTML attributes. For example, if an Angular component has an input property @Input('myInputProp'), it would be converted to a custom element attribute my-input-prop[2][5].
Component Outputs to Custom Element Events:
Angular's @Output() properties are mapped to custom events in the custom element. This enables the custom element to dispatch events that can be listened to by the outer environment. For instance, if a component has an output property @Output() valueChanged = new EventEmitter(), in the custom element, this would be dispatched as a custom event named valueChanged[2][5].
Lifecycle Hooks and Methods:
Angular lifecycle hooks and methods are preserved in the custom element. This includes hooks like ngOnInit() and ngOnDestroy(), ensuring that the custom element behaves similarly to how the component would within an Angular environment[5][12].
Encapsulation and Styling:
Styles defined within an Angular component using styles or styleUrls are encapsulated within the custom element using Shadow DOM. This ensures that styles are scoped to the component and do not leak to the outer HTML[8].
Registration and Usage:
Once the Angular component is transformed into a custom element using the createCustomElement() function from the @angular/elements package, it must be registered with the browser's CustomElementRegistry using customElements.define(). This function takes a tag name and the constructor of the custom element, linking the component to the DOM API[5][18].
Data Binding and Attribute Reflection:
To ensure that changes in the component's properties are reflected as changes in the corresponding attributes of the custom element (and vice versa), Angular handles the ...
