Angular 面试题与答案

问题 1. What are angular elements?

Angular elements are Angular components packaged as custom elements(a web standard for defining new HTML elements in a framework-agnostic way). Angular Elements hosts an Angular component, providing a bridge between the data and logic defined in the component and standard DOM APIs, thus, providing a way to use Angular components in non-Angular environments.

问题 2. What are custom elements in Angular?

Custom elements (or Web Components) are a Web Platform feature which extends HTML by allowing you to define a tag whose content is created and controlled by JavaScript code. The browser maintains a CustomElementRegistry of defined custom elements, which maps an instantiable JavaScript class to an HTML tag. Currently this feature is supported by Chrome, Firefox, Opera, and Safari, and available in other browsers through polyfills.

问题 3. Do I need to bootstrap custom elements in Angular?

No, custom elements bootstrap (or start) automatically when they are added to the DOM, and are automatically destroyed when removed from the DOM. Once a custom element is added to the DOM for any page, it looks and behaves like any other HTML element, and does not require any special knowledge of Angular.

问题 4. What are the mapping rules between Angular component and custom element?

The Component properties and logic maps directly into HTML attributes and the browser's event system. Let us describe them in two steps,

1. The createCustomElement() API parses the component input properties with corresponding attributes for the custom element. For example, component @Input('myInputProp') converted as custom element attribute my-input-prop.
2. The Component outputs are dispatched as HTML Custom Events, with the name of the custom event matching the output name. For example, component @Output() valueChanged = new EventEmitter() converted as custom element with dispatch event as "valueChanged".

问题 5. What is Angular Framework?

Angular is a TypeScript-based open-source front-end platform that makes it easy to build web, mobile and desktop applications. The major features of this framework include declarative templates, dependency injection, end to end tooling which ease application development.