Custom Elements are a fundamental part of the Web Components technology suite, allowing developers to create reusable, encapsulated HTML tags for use in web pages and web apps. Angular leverages this technology through the @angular/elements package, which enables the creation of Angular components as Custom Elements. Here’s a detailed explanation of how Custom Elements work internally, particularly when implemented using Angular:
1. Component Registration
The process begins with the registration of the Angular component as a Custom Element. This is achieved using the createCustomElement() function from the @angular/elements package. This function transforms an Angular component into a class that extends HTMLElement, which is the standard class for HTML elements[1][2][3].
2. Creating the Custom Element Class
The createCustomElement() function takes an Angular component and a configuration object, and returns a new constructor function. This constructor function is used to instantiate the custom element. The configuration object typically includes an injector, which is used to provide the dependencies needed by the Angular component[1][2][3].
3. Defining the Custom Element
Once the custom element class is created, it must be registered with the browser's CustomElementRegistry. This is done using the customElements.define() method, where you specify a tag name for the new element and the constructor function returned by createCustomElement(). This step makes the new custom element available for use in HTML documents[1][2][3].
4. Lifecycle Hooks Integration
Custom Elements have their own lifecycle hooks such as connectedCallback, disconnectedCallback, attributeChangedCallback, etc. Angular integrates these lifecycle hooks with its own component lifecycle. For instance, when a custom element is added to the DOM (connectedCallback), Angular initializes the component and attaches it to the change detection tree of the application[2][3].
5. Data Binding and Attribute Reflection
Angular's data binding capabilities are adapted to work with Custom Elements. Input properties of the Angular component are linked to attributes of the custom element. Changes to attributes automatically update the component properties, and vice versa, thanks to Angular's change detection mechanism. This synchronization allows the custom element to react dynamically to data changes just like standard Angular components[1][2][3].
6. Event Handling
Output properties of the Angular component are exposed as Custom Events in the Custom Element. When an event is emitted by the Angular component, it is dispatched a...
