@loopback/docs

--- lang: en title: 'API docs: core' keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI sidebar: lb4_sidebar editurl: https://github.com/loopbackio/loopback-next/tree/master/packages/core permalink: /doc/en/lb4/apidocs.core.html ---  [Home](./index.md) > [@loopback/core](./core.md) ## core package The core foundation for LoopBack 4. It can also serve as the platform to build large-scale Node.js applications and frameworks. ## Remarks For examples of how to leverage `@loopback/core` to build composable and extensible projects, check out the [core tutorial](https://loopback.io/doc/en/lb4/core-tutorial.html). ## Classes <table><thead><tr><th> Class </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [Application](./core.application.md) </td><td markdown="1"> Application is the container for various types of artifacts, such as components, servers, controllers, repositories, datasources, connectors, and models. </td></tr> <tr><td markdown="1"> [LifeCycleObserverRegistry](./core.lifecycleobserverregistry.md) </td><td markdown="1"> A context-based registry for life cycle observers </td></tr> </tbody></table> ## Functions <table><thead><tr><th> Function </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [addExtension(context, extensionPointName, extensionClass, options)](./core.addextension.md) </td><td markdown="1"> Register an extension for the given extension point to the context </td></tr> <tr><td markdown="1"> [asLifeCycleObserver(binding)](./core.aslifecycleobserver.md) </td><td markdown="1"> A `BindingTemplate` function to configure the binding as life cycle observer by tagging it with `CoreTags.LIFE_CYCLE_OBSERVER`. </td></tr> <tr><td markdown="1"> [asService(serviceInterface)](./core.asservice.md) </td><td markdown="1"> Create a binding template for a service interface </td></tr> <tr><td markdown="1"> [createServiceBinding(cls, options)](./core.createservicebinding.md) </td><td markdown="1"> Create a service binding from a class or provider </td></tr> <tr><td markdown="1"> [extensionFilter(extensionPointNames)](./core.extensionfilter.md) </td><td markdown="1"> A factory function to create binding filter for extensions of a named extension point </td></tr> <tr><td markdown="1"> [extensionFor(extensionPointNames)](./core.extensionfor.md) </td><td markdown="1"> A factory function to create binding template for extensions of the given extension point </td></tr> <tr><td markdown="1"> [extensionPoint(name, specs)](./core.extensionpoint.md) </td><td markdown="1"> Decorate a class as a named extension point. If the decoration is not present, the name of the class will be used. </td></tr> <tr><td markdown="1"> [extensions(extensionPointName, metadata)](./core.extensions.md) </td><td markdown="1"> Shortcut to inject extensions for the given extension point. </td></tr> <tr><td markdown="1"> [filterByServiceInterface(serviceInterface)](./core.filterbyserviceinterface.md) </td><td markdown="1"> Create a binding filter by service class </td></tr> <tr><td markdown="1"> [isLifeCycleObserver(obj)](./core.islifecycleobserver.md) </td><td markdown="1"> Test if an object implements LifeCycleObserver </td></tr> <tr><td markdown="1"> [isLifeCycleObserverClass(ctor)](./core.islifecycleobserverclass.md) </td><td markdown="1"> Test if a class implements LifeCycleObserver </td></tr> <tr><td markdown="1"> [lifeCycleObserver(group, specs)](./core.lifecycleobserver.md) </td><td markdown="1"> Sugar decorator to mark a class as life cycle observer </td></tr> <tr><td markdown="1"> [mountComponent(app, component)](./core.mountcomponent.md) </td><td markdown="1"> Mount a component to an Application. </td></tr> <tr><td markdown="1"> [service(serviceInterface, metadata)](./core.service.md) </td><td markdown="1"> `@service` injects a service instance that matches the class or interface. </td></tr> </tbody></table> ## Interfaces <table><thead><tr><th> Interface </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [ApplicationConfig](./core.applicationconfig.md) </td><td markdown="1"> Configuration for application </td></tr> <tr><td markdown="1"> [ApplicationMetadata](./core.applicationmetadata.md) </td><td markdown="1"> Type description for `package.json` </td></tr> <tr><td markdown="1"> [ClassMap](./core.classmap.md) </td><td markdown="1"> A map of classes to be bound to a context </td></tr> <tr><td markdown="1"> [Component](./core.component.md) </td><td markdown="1"> A component declares a set of artifacts so that they can be contributed to an application as a group </td></tr> <tr><td markdown="1"> [LifeCycleObserver](./core.lifecycleobserver.md) </td><td markdown="1"> Observers to handle life cycle init/start/stop events </td></tr> <tr><td markdown="1"> [ProviderMap](./core.providermap.md) </td><td markdown="1"> A map of provider classes to be bound to a context </td></tr> <tr><td markdown="1"> [Server](./core.server.md) </td><td markdown="1"> Defines the requirements to implement a Server for LoopBack applications: start() : Promise<void> stop() : Promise<void> It is recommended that each Server implementation creates its own child Context, which inherits from the parent Application context. This way, any Server-specific bindings will remain local to the Server instance, and will avoid polluting its parent module scope. </td></tr> <tr><td markdown="1"> [ServiceOptions](./core.serviceoptions.md) </td><td markdown="1"> Options to register a service binding </td></tr> </tbody></table> ## Namespaces <table><thead><tr><th> Namespace </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [CoreBindings](./core.corebindings.md) </td><td markdown="1"> Namespace for core binding keys </td></tr> <tr><td markdown="1"> [CoreTags](./core.coretags.md) </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [extensions](./core.extensions.md) </td><td markdown="1"> </td></tr> </tbody></table> ## Variables <table><thead><tr><th> Variable </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [DEFAULT\_ORDERED\_GROUPS](./core.default_ordered_groups.md) </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [lifeCycleObserverFilter](./core.lifecycleobserverfilter.md) </td><td markdown="1"> Find all life cycle observer bindings. By default, a binding tagged with `CoreTags.LIFE_CYCLE_OBSERVER`. It's used as `BindingFilter`. </td></tr> </tbody></table> ## Type Aliases <table><thead><tr><th> Type Alias </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [ControllerClass](./core.controllerclass.md) </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [LifeCycleObserverGroup](./core.lifecycleobservergroup.md) </td><td markdown="1"> A group of life cycle observers </td></tr> <tr><td markdown="1"> [LifeCycleObserverOptions](./core.lifecycleobserveroptions.md) </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [MixinTarget](./core.mixintarget.md) </td><td markdown="1"> A replacement for `typeof Target` to be used in mixin class definitions. This is a workaround for TypeScript limitation described in - https://github.com/microsoft/TypeScript/issues/17293 - https://github.com/microsoft/TypeScript/issues/17744 - https://github.com/microsoft/TypeScript/issues/36060 </td></tr> <tr><td markdown="1"> [ServiceInterface](./core.serviceinterface.md) </td><td markdown="1"> Representing an interface for services. In TypeScript, the `interface` does not have reflections at runtime. We use a string, a symbol or a Function as the type for the service interface. </td></tr> <tr><td markdown="1"> [ServiceOrProviderClass](./core.serviceorproviderclass.md) </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [ShutdownOptions](./core.shutdownoptions.md) </td><td markdown="1"> Options to set up application shutdown </td></tr> </tbody></table>