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Components play an important part in the extensibility of LoopBack 4. A Component makes it easy for independent developers to contribute additional features to LoopBack. Components serve as a vehicle to group extension contributions such as Context Bindings and various artifacts to allow easier extensibility of your Application.

A typical LoopBack component is an npm package exporting a Component class which can be added to your application.

import {RestApplication} from '@loopback/rest';
import {AuthenticationComponent} from '@loopback/authentication';

const app = new RestApplication();
// Add component to Application, which provides bindings used to resolve
// authenticated requests in a Sequence.

Components can contribute the following items:

LoopBack 4 was built with extensibility in mind and this includes Components, which can be allowed to contribute additional artifacts by adding a Mixin to your Application class. This doesn’t change how a Component is registered (app.component()) but it enables the Component to contribute additional artifacts. For example:

  • Repositories can be contributed by a Component by adding RepositoryMixin from @loopback/repository to your Application
  • Booters can be contributed by a Component by adding BootMixin from @loopback/boot to your Application

Note: Always check a component’s instructions to see if it requires the use of a Mixin. A Mixin may automatically register a Component, saving you the trouble of having to do so manually. Again it’s best to check the documentation for the given Component / Mixin.