--- lang: en title: 'API docs: context.binding' keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI sidebar: lb4_sidebar editurl: https://github.com/loopbackio/loopback-next/tree/master/packages/context permalink: /doc/en/lb4/apidocs.context.binding.html --- [Home](./index.md) > [@loopback/context](./context.md) > [Binding](./context.binding.md) ## Binding class Binding represents an entry in the `Context`. Each binding has a key and a corresponding value getter. **Signature:** ```typescript export declare class Binding extends EventEmitter ``` **Extends:** EventEmitter ## Constructors
Constructor Modifiers Description
[(constructor)(key, isLocked)](./context.binding._constructor_.md) Constructs a new instance of the `Binding` class
## Properties
Property Modifiers Type Description
[isLocked](./context.binding.islocked.md) boolean
[key](./context.binding.key.md) `readonly` string Key of the binding
[providerConstructor](./context.binding.providerconstructor.md) `readonly` [Constructor](./context.constructor.md)<[Provider](./context.provider.md)<T>> \| undefined For bindings bound via `toProvider()`, this property contains the constructor function of the provider class
[scope](./context.binding.scope.md) `readonly` [BindingScope](./context.bindingscope.md) Scope of the binding to control how the value is cached/shared
[source](./context.binding.source.md) `readonly` [BindingSource](./context.bindingsource.md)<T> \| undefined
[tagMap](./context.binding.tagmap.md) `readonly` [TagMap](./context.tagmap.md) Map for tag name/value pairs
[tagNames](./context.binding.tagnames.md) `readonly` string\[\] Get an array of tag names
[type](./context.binding.type.md) `readonly` [BindingType](./context.bindingtype.md) \| undefined Type of the binding value getter
[valueConstructor](./context.binding.valueconstructor.md) `readonly` [Constructor](./context.constructor.md)<T> \| undefined For bindings bound via `toClass()`, this property contains the constructor function of the class
## Methods
Method Modifiers Description
[apply(templateFns)](./context.binding.apply.md) Apply one or more template functions to set up the binding with scope, tags, and other attributes as a group.
[applyDefaultScope(scope)](./context.binding.applydefaultscope.md) Apply default scope to the binding. It only changes the scope if it's not set yet
[bind(key)](./context.binding.bind.md) `static` A static method to create a binding so that we can do `Binding.bind('foo').to('bar');` as `new Binding('foo').to('bar')` is not easy to read.
[configure(key)](./context.binding.configure.md) `static` Create a configuration binding for the given key
[getValue(ctx, session)](./context.binding.getvalue.md) This is an internal function optimized for performance. Users should use `@inject(key)` or `ctx.get(key)` instead. Get the value bound to this key. Depending on `isSync`, this function returns either: - the bound value - a promise of the bound value Consumers wishing to consume sync values directly should use `isPromiseLike` to check the type of the returned value to decide how to handle it.
[getValue(ctx, options)](./context.binding.getvalue_1.md) Returns a value or promise for this binding in the given context. The resolved value can be `undefined` if `optional` is set to `true` in `options`.
[inScope(scope)](./context.binding.inscope.md) Set the binding scope
[inspect(options)](./context.binding.inspect.md) Inspect the binding to return a json representation of the binding information
[lock()](./context.binding.lock.md) Lock the binding so that it cannot be rebound
[on(eventName, listener)](./context.binding.on.md) The "changed" event is emitted by methods such as `tag`, `inScope`, `to`, and `toClass`.
[on(event, listener)](./context.binding.on_1.md)
[once(eventName, listener)](./context.binding.once.md) The "changed" event is emitted by methods such as `tag`, `inScope`, `to`, and `toClass`.
[once(event, listener)](./context.binding.once_1.md)
[refresh(ctx)](./context.binding.refresh.md) Invalidate the binding cache so that its value will be reloaded next time. This is useful to force reloading a cached value when its configuration or dependencies are changed. \*\*WARNING\*\*: The state held in the cached value will be gone.
[tag(tags)](./context.binding.tag.md) Tag the binding with names or name/value objects. A tag has a name and an optional value. If not supplied, the tag name is used as the value.
[to(value)](./context.binding.to.md) Bind the key to a constant value. The value must be already available at binding time, it is not allowed to pass a Promise instance.
[toAlias(keyWithPath)](./context.binding.toalias.md) Bind the key to an alias of another binding
[toClass(ctor)](./context.binding.toclass.md) Bind the key to an instance of the given class.
[toDynamicValue(factory)](./context.binding.todynamicvalue.md) Bind the key to a computed (dynamic) value.
[toInjectable(ctor)](./context.binding.toinjectable.md) Bind to a class optionally decorated with `@injectable`. Based on the introspection of the class, it calls `toClass/toProvider/toDynamicValue` internally. The current binding key will be preserved (not being overridden by the key inferred from the class or options). This is similar to [createBindingFromClass()](./context.createbindingfromclass.md) but applies to an existing binding.
[toJSON()](./context.binding.tojson.md) Convert to a plain JSON object
[toProvider(providerClass)](./context.binding.toprovider.md) Bind the key to a value computed by a Provider. \*
[unlock()](./context.binding.unlock.md) Unlock the binding