In AngularJS, directives and components are both used to extend HTML with custom behavior, but they differ in some important ways.
A directive is a marker on an HTML element that tells AngularJS to attach a specific behavior to that element. Directives can be used to create reusable HTML components, apply behavior to existing elements, or modify the behavior of AngularJS itself. Directives are defined using the directive() function, and typically include a link function that provides the directive's behavior.
A component is a special type of directive that encapsulates both the behavior and the view of a custom HTML element. Components are used to create reusable UI elements, such as buttons, forms, or cards. Components can have their own templates, controllers, and styles, making them a self-contained unit of functionality. Components are defined using the component() function, which takes a configuration object that defines the component's properties and behavior.
The main differences between directives and components in AngularJS are:
Scope: Directives can use the scope of the parent element, the isolate scope, or no scope at all. Components use an isolate scope by default, which makes it easier to reason about the component's behavior and data.
Template: Directives can manipulate the existing HTML, but they don't have their own template. Components have their own templates, which allows them to encapsulate their own markup and styles.
Controller: Directives can have their own controllers, but they don't have to. Components must have their own controller, which is used to define the component's behavior and manage its data.
Reusability: Directives can be used to create reusable behaviors, but they require more configuration to make them reusable as UI components. Components are designed to be reusable UI elements, and have built-in features for encapsulating their own behavior, markup, and styles.
Overall, both directives and components are important tools for building custom functionality in AngularJS, and the choice between them depends on the specific needs and requirements of the application being developed.