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Overview

Components play an important role 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.

Apart from its own properties, Component class can have the following properties:

  • controllers - An array of controller classes.
  • providers - A map of providers to be bound to the application context.
  • classes - A map of TypeScipt classes to be bound to the application context.
  • servers - A map of name/class pairs for servers.
  • lifeCycleObservers - An array of life cycle observers.
  • bindings - An array of bindings to be aded to the application context. A good example of using bindings to extend the functionality of a LoopBack 4 app is contributing an additional body parser.

These properties contribute to the application to add additional features and capabilities.

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

See Using components and Creating components for more information.