@loopback/docs

--- 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<T = BoundValue> extends EventEmitter ``` **Extends:** EventEmitter ## Constructors <table><thead><tr><th> Constructor </th><th> Modifiers </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [(constructor)(key, isLocked)](./context.binding._constructor_.md) </td><td markdown="1"> </td><td markdown="1"> Constructs a new instance of the `Binding` class </td></tr> </tbody></table> ## Properties <table><thead><tr><th> Property </th><th> Modifiers </th><th> Type </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [isLocked](./context.binding.islocked.md) </td><td markdown="1"> </td><td markdown="1"> boolean </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [key](./context.binding.key.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> string </td><td markdown="1"> Key of the binding </td></tr> <tr><td markdown="1"> [providerConstructor](./context.binding.providerconstructor.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [Constructor](./context.constructor.md)<[Provider](./context.provider.md)<T>> \| undefined </td><td markdown="1"> For bindings bound via `toProvider()`, this property contains the constructor function of the provider class </td></tr> <tr><td markdown="1"> [scope](./context.binding.scope.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [BindingScope](./context.bindingscope.md) </td><td markdown="1"> Scope of the binding to control how the value is cached/shared </td></tr> <tr><td markdown="1"> [source](./context.binding.source.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [BindingSource](./context.bindingsource.md)<T> \| undefined </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [tagMap](./context.binding.tagmap.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [TagMap](./context.tagmap.md) </td><td markdown="1"> Map for tag name/value pairs </td></tr> <tr><td markdown="1"> [tagNames](./context.binding.tagnames.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> string\[\] </td><td markdown="1"> Get an array of tag names </td></tr> <tr><td markdown="1"> [type](./context.binding.type.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [BindingType](./context.bindingtype.md) \| undefined </td><td markdown="1"> Type of the binding value getter </td></tr> <tr><td markdown="1"> [valueConstructor](./context.binding.valueconstructor.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [Constructor](./context.constructor.md)<T> \| undefined </td><td markdown="1"> For bindings bound via `toClass()`, this property contains the constructor function of the class </td></tr> </tbody></table> ## Methods <table><thead><tr><th> Method </th><th> Modifiers </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [apply(templateFns)](./context.binding.apply.md) </td><td markdown="1"> </td><td markdown="1"> Apply one or more template functions to set up the binding with scope, tags, and other attributes as a group. </td></tr> <tr><td markdown="1"> [applyDefaultScope(scope)](./context.binding.applydefaultscope.md) </td><td markdown="1"> </td><td markdown="1"> Apply default scope to the binding. It only changes the scope if it's not set yet </td></tr> <tr><td markdown="1"> [bind(key)](./context.binding.bind.md) </td><td markdown="1"> `static` </td><td markdown="1"> 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. </td></tr> <tr><td markdown="1"> [configure(key)](./context.binding.configure.md) </td><td markdown="1"> `static` </td><td markdown="1"> Create a configuration binding for the given key </td></tr> <tr><td markdown="1"> [getValue(ctx, session)](./context.binding.getvalue.md) </td><td markdown="1"> </td><td markdown="1"> 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. </td></tr> <tr><td markdown="1"> [getValue(ctx, options)](./context.binding.getvalue_1.md) </td><td markdown="1"> </td><td markdown="1"> 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`. </td></tr> <tr><td markdown="1"> [inScope(scope)](./context.binding.inscope.md) </td><td markdown="1"> </td><td markdown="1"> Set the binding scope </td></tr> <tr><td markdown="1"> [inspect(options)](./context.binding.inspect.md) </td><td markdown="1"> </td><td markdown="1"> Inspect the binding to return a json representation of the binding information </td></tr> <tr><td markdown="1"> [lock()](./context.binding.lock.md) </td><td markdown="1"> </td><td markdown="1"> Lock the binding so that it cannot be rebound </td></tr> <tr><td markdown="1"> [on(eventName, listener)](./context.binding.on.md) </td><td markdown="1"> </td><td markdown="1"> The "changed" event is emitted by methods such as `tag`, `inScope`, `to`, and `toClass`. </td></tr> <tr><td markdown="1"> [on(event, listener)](./context.binding.on_1.md) </td><td markdown="1"> </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [once(eventName, listener)](./context.binding.once.md) </td><td markdown="1"> </td><td markdown="1"> The "changed" event is emitted by methods such as `tag`, `inScope`, `to`, and `toClass`. </td></tr> <tr><td markdown="1"> [once(event, listener)](./context.binding.once_1.md) </td><td markdown="1"> </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [refresh(ctx)](./context.binding.refresh.md) </td><td markdown="1"> </td><td markdown="1"> 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. </td></tr> <tr><td markdown="1"> [tag(tags)](./context.binding.tag.md) </td><td markdown="1"> </td><td markdown="1"> 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. </td></tr> <tr><td markdown="1"> [to(value)](./context.binding.to.md) </td><td markdown="1"> </td><td markdown="1"> 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. </td></tr> <tr><td markdown="1"> [toAlias(keyWithPath)](./context.binding.toalias.md) </td><td markdown="1"> </td><td markdown="1"> Bind the key to an alias of another binding </td></tr> <tr><td markdown="1"> [toClass(ctor)](./context.binding.toclass.md) </td><td markdown="1"> </td><td markdown="1"> Bind the key to an instance of the given class. </td></tr> <tr><td markdown="1"> [toDynamicValue(factory)](./context.binding.todynamicvalue.md) </td><td markdown="1"> </td><td markdown="1"> Bind the key to a computed (dynamic) value. </td></tr> <tr><td markdown="1"> [toInjectable(ctor)](./context.binding.toinjectable.md) </td><td markdown="1"> </td><td markdown="1"> 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. </td></tr> <tr><td markdown="1"> [toJSON()](./context.binding.tojson.md) </td><td markdown="1"> </td><td markdown="1"> Convert to a plain JSON object </td></tr> <tr><td markdown="1"> [toProvider(providerClass)](./context.binding.toprovider.md) </td><td markdown="1"> </td><td markdown="1"> Bind the key to a value computed by a Provider. \* </td></tr> <tr><td markdown="1"> [unlock()](./context.binding.unlock.md) </td><td markdown="1"> </td><td markdown="1"> Unlock the binding </td></tr> </tbody></table>