@loopback/docs

--- lang: en title: 'API docs: context.context' 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.context.html ---  [Home](./index.md) > [@loopback/context](./context.md) > [Context](./context.context.md) ## Context class Context provides an implementation of Inversion of Control (IoC) container **Signature:** ```typescript export declare class Context 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)(\_parent, name)](./context.context._constructor_.md) </td><td markdown="1"> </td><td markdown="1"> Create a new context. </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"> [\_debug](./context.context._debug.md) </td><td markdown="1"> `protected` </td><td markdown="1"> Debugger </td><td markdown="1"> A debug function which can be overridden by subclasses. </td></tr> <tr><td markdown="1"> [\_parent?](./context.context._parent.md) </td><td markdown="1"> `protected` </td><td markdown="1"> [Context](./context.context.md) </td><td markdown="1"> _(Optional)_ Parent context </td></tr> <tr><td markdown="1"> [configResolver](./context.context.configresolver.md) </td><td markdown="1"> `protected` </td><td markdown="1"> [ConfigurationResolver](./context.configurationresolver.md) </td><td markdown="1"> Configuration resolver </td></tr> <tr><td markdown="1"> [name](./context.context.name.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> string </td><td markdown="1"> Name of the context </td></tr> <tr><td markdown="1"> [registry](./context.context.registry.md) </td><td markdown="1"> `protected` `readonly` </td><td markdown="1"> Map<string, [Binding](./context.binding.md)> </td><td markdown="1"> Key to binding map as the internal registry </td></tr> <tr><td markdown="1"> [scope](./context.context.scope.md) </td><td markdown="1"> </td><td markdown="1"> [BindingScope](./context.bindingscope.md) </td><td markdown="1"> Scope for binding resolution </td></tr> <tr><td markdown="1"> [subscriptionManager](./context.context.subscriptionmanager.md) </td><td markdown="1"> `readonly` </td><td markdown="1"> [ContextSubscriptionManager](./context.contextsubscriptionmanager.md) </td><td markdown="1"> Manager for observer subscriptions </td></tr> <tr><td markdown="1"> [tagIndexer](./context.context.tagindexer.md) </td><td markdown="1"> `protected` `readonly` </td><td markdown="1"> ContextTagIndexer </td><td markdown="1"> Indexer for bindings by tag </td></tr> </tbody></table> ## Methods <table><thead><tr><th> Method </th><th> Modifiers </th><th> Description </th></tr></thead> <tbody><tr><td markdown="1"> [\_findByTagIndex(tag)](./context.context._findbytagindex.md) </td><td markdown="1"> `protected` </td><td markdown="1"> Find bindings by tag leveraging indexes </td></tr> <tr><td markdown="1"> [\_mergeWithParent(childList, parentList)](./context.context._mergewithparent.md) </td><td markdown="1"> `protected` </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [add(binding)](./context.context.add.md) </td><td markdown="1"> </td><td markdown="1"> Add a binding to the context. If a locked binding already exists with the same key, an error will be thrown. </td></tr> <tr><td markdown="1"> [bind(key)](./context.context.bind.md) </td><td markdown="1"> </td><td markdown="1"> Create a binding with the given key in the context. If a locked binding already exists with the same key, an error will be thrown. </td></tr> <tr><td markdown="1"> [close()](./context.context.close.md) </td><td markdown="1"> </td><td markdown="1"> Close the context: clear observers, stop notifications, and remove event listeners from its parent context. </td></tr> <tr><td markdown="1"> [configure(key)](./context.context.configure.md) </td><td markdown="1"> </td><td markdown="1"> Create a corresponding binding for configuration of the target bound by the given key in the context. For example, `ctx.configure('controllers.MyController').to({x: 1})` will create binding `controllers.MyController:$config` with value `{x: 1}`. </td></tr> <tr><td markdown="1"> [contains(key)](./context.context.contains.md) </td><td markdown="1"> </td><td markdown="1"> Check if a binding exists with the given key in the local context without delegating to the parent context </td></tr> <tr><td markdown="1"> [createView(filter, comparator, options)](./context.context.createview.md) </td><td markdown="1"> </td><td markdown="1"> Create a view of the context chain with the given binding filter </td></tr> <tr><td markdown="1"> [debug(args)](./context.context.debug.md) </td><td markdown="1"> `protected` </td><td markdown="1"> Wrap the debug statement so that it always print out the context name as the prefix </td></tr> <tr><td markdown="1"> [emitError(err)](./context.context.emiterror.md) </td><td markdown="1"> </td><td markdown="1"> Emit an `error` event </td></tr> <tr><td markdown="1"> [emitEvent(type, event)](./context.context.emitevent.md) </td><td markdown="1"> </td><td markdown="1"> A strongly-typed method to emit context events </td></tr> <tr><td markdown="1"> [find(pattern)](./context.context.find.md) </td><td markdown="1"> </td><td markdown="1"> Find bindings using a key pattern or filter function </td></tr> <tr><td markdown="1"> [findByTag(tagFilter)](./context.context.findbytag.md) </td><td markdown="1"> </td><td markdown="1"> Find bindings using the tag filter. If the filter matches one of the binding tags, the binding is included. </td></tr> <tr><td markdown="1"> [findOrCreateBinding(key, policy)](./context.context.findorcreatebinding.md) </td><td markdown="1"> </td><td markdown="1"> Find or create a binding for the given key </td></tr> <tr><td markdown="1"> [get(keyWithPath, session)](./context.context.get.md) </td><td markdown="1"> </td><td markdown="1"> Get the value bound to the given key, throw an error when no value is bound for the given key. </td></tr> <tr><td markdown="1"> [get(keyWithPath, options)](./context.context.get_1.md) </td><td markdown="1"> </td><td markdown="1"> Get the value bound to the given key, optionally return a (deep) property of the bound value. </td></tr> <tr><td markdown="1"> [getBinding(key)](./context.context.getbinding.md) </td><td markdown="1"> </td><td markdown="1"> Look up a binding by key in the context and its ancestors. If no matching binding is found, an error will be thrown. </td></tr> <tr><td markdown="1"> [getBinding(key, options)](./context.context.getbinding_1.md) </td><td markdown="1"> </td><td markdown="1"> Look up a binding by key in the context and its ancestors. If no matching binding is found and `options.optional` is not set to true, an error will be thrown. </td></tr> <tr><td markdown="1"> [getConfig(key, propertyPath, resolutionOptions)](./context.context.getconfig.md) </td><td markdown="1"> </td><td markdown="1"> Resolve configuration for the binding by key </td></tr> <tr><td markdown="1"> [getConfigAsValueOrPromise(key, propertyPath, resolutionOptions)](./context.context.getconfigasvalueorpromise.md) </td><td markdown="1"> </td><td markdown="1"> Get the value or promise of configuration for a given binding by key </td></tr> <tr><td markdown="1"> [getConfigSync(key, propertyPath, resolutionOptions)](./context.context.getconfigsync.md) </td><td markdown="1"> </td><td markdown="1"> Resolve configuration synchronously for the binding by key </td></tr> <tr><td markdown="1"> [getDebugNamespace()](./context.context.getdebugnamespace.md) </td><td markdown="1"> `protected` </td><td markdown="1"> Get the debug namespace for the context class. Subclasses can override this method to supply its own namespace. </td></tr> <tr><td markdown="1"> [getOwnerContext(keyOrBinding)](./context.context.getownercontext.md) </td><td markdown="1"> </td><td markdown="1"> Get the owning context for a binding or its key </td></tr> <tr><td markdown="1"> [getResolutionContext(binding)](./context.context.getresolutioncontext.md) </td><td markdown="1"> </td><td markdown="1"> Locate the resolution context for the given binding. Only bindings in the resolution context and its ancestors are visible as dependencies to resolve the given binding </td></tr> <tr><td markdown="1"> [getScopedContext(scope)](./context.context.getscopedcontext.md) </td><td markdown="1"> </td><td markdown="1"> Get the context matching the scope </td></tr> <tr><td markdown="1"> [getSync(keyWithPath, session)](./context.context.getsync.md) </td><td markdown="1"> </td><td markdown="1"> Get the synchronous value bound to the given key, optionally return a (deep) property of the bound value. This method throws an error if the bound value requires async computation (returns a promise). You should never rely on sync bindings in production code. </td></tr> <tr><td markdown="1"> [getSync(keyWithPath, options)](./context.context.getsync_1.md) </td><td markdown="1"> </td><td markdown="1"> Get the synchronous value bound to the given key, optionally return a (deep) property of the bound value. This method throws an error if the bound value requires async computation (returns a promise). You should never rely on sync bindings in production code. </td></tr> <tr><td markdown="1"> [inspect(options)](./context.context.inspect.md) </td><td markdown="1"> </td><td markdown="1"> Inspect the context and dump out a JSON object representing the context hierarchy </td></tr> <tr><td markdown="1"> [isBound(key)](./context.context.isbound.md) </td><td markdown="1"> </td><td markdown="1"> Check if a key is bound in the context or its ancestors </td></tr> <tr><td markdown="1"> [isSubscribed(observer)](./context.context.issubscribed.md) </td><td markdown="1"> </td><td markdown="1"> Check if an observer is subscribed to this context </td></tr> <tr><td markdown="1"> [isVisibleTo(ctx)](./context.context.isvisibleto.md) </td><td markdown="1"> </td><td markdown="1"> Check if this context is visible (same or ancestor) to the given one </td></tr> <tr><td markdown="1"> [on(eventName, listener)](./context.context.on.md) </td><td markdown="1"> </td><td markdown="1"> The "bind" event is emitted when a new binding is added to the context. The "unbind" event is emitted when an existing binding is removed. </td></tr> <tr><td markdown="1"> [on(event, listener)](./context.context.on_1.md) </td><td markdown="1"> </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [once(eventName, listener)](./context.context.once.md) </td><td markdown="1"> </td><td markdown="1"> The "bind" event is emitted when a new binding is added to the context. The "unbind" event is emitted when an existing binding is removed. </td></tr> <tr><td markdown="1"> [once(event, listener)](./context.context.once_1.md) </td><td markdown="1"> </td><td markdown="1"> </td></tr> <tr><td markdown="1"> [setupConfigurationResolverIfNeeded()](./context.context.setupconfigurationresolverifneeded.md) </td><td markdown="1"> `protected` </td><td markdown="1"> Set up the configuration resolver if needed </td></tr> <tr><td markdown="1"> [subscribe(observer)](./context.context.subscribe.md) </td><td markdown="1"> </td><td markdown="1"> Add a context event observer to the context </td></tr> <tr><td markdown="1"> [toJSON()](./context.context.tojson.md) </td><td markdown="1"> </td><td markdown="1"> Create a plain JSON object for the context </td></tr> <tr><td markdown="1"> [unbind(key)](./context.context.unbind.md) </td><td markdown="1"> </td><td markdown="1"> Unbind a binding from the context. No parent contexts will be checked. </td></tr> <tr><td markdown="1"> [unsubscribe(observer)](./context.context.unsubscribe.md) </td><td markdown="1"> </td><td markdown="1"> Remove the context event observer from the context </td></tr> </tbody></table>