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Angular error NG0203 means inject() ran when no dependency-injection context was active. Move the call into a supported synchronous context—usually a DI-managed class field initializer or constructor—or use a saved Injector for a later lookup. This is a context-timing error, not a missing-provider error. Angular’s NG0203 guide explains the error.
What NG0203 means
Angular makes the current injector available only while code is running in an injection context. Calling inject(Token) outside that context produces NG0203. The key question is where and when the call executes—not whether Angular has a provider for the token. Angular’s injection-context guide describes the supported contexts.
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Where can you call inject()?
Supported locations
- A constructor or field initializer of a class instantiated by Angular’s dependency-injection system.
- A provider’s
useFactoryfunction or anInjectionTokenfactory. - A function called by an Angular API that supplies an injection context, such as a functional route guard.
- A synchronous callback passed to
runInInjectionContext(injector, callback). - In tests, a callback passed to
TestBed.runInInjectionContext().
See the inject API reference for the API’s call-site requirements.
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- An ordinary instance method called after the class has been constructed, including lifecycle hooks such as
ngOnInit. - A callback that runs later, such as one scheduled with
setTimeoutorPromise.then. - Code that runs after an
await.
These calls occur after the original synchronous injection context has ended. Being inside a class or a function that was initially called from an injection context does not keep that context active for later work.
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How to find the failing call
- Read the NG0203 stack trace and locate the
inject()call that triggered the error. - Trace callers back to see whether that call runs during DI-managed construction, a factory, or another supported context—or instead runs in a later method or callback.
- Choose a fix based on when the token is needed: capture it during construction for ordinary later use, retrieve it through a saved
Injectorfor deferred lookup, or establish a synchronous context for a callback that must callinject().
Angular’s dependency-injection troubleshooting guide also shows how to diagnose and resolve this class of error.
Choose the right fix
| Need | Approach |
|---|---|
| A class needs a dependency in methods or lifecycle hooks | Capture it in a field initializer or constructor and use the saved reference. |
| A later method or callback needs a token that was not captured earlier | Capture an Injector in a valid context, then call injector.get(Token) when needed. |
A callback itself must use inject() |
Run its synchronous work with runInInjectionContext(injector, callback). |
Test code needs to call inject() |
Use TestBed.runInInjectionContext(() => ...). |
Capture a dependency during construction
This is the usual fix when a class needs a service later. Move the injection to a field initializer or constructor, then use the saved value in methods such as ngOnInit. Angular’s error page recommends moving the call to an allowed place, usually a constructor or field initializer: NG0203: inject() must be called from an injection context.
Use an injector for deferred lookup
If the token should be selected or retrieved later, inject an Injector while the class is being constructed and call injector.get(Token) at the later point. This avoids calling the context-dependent inject() function after construction. The troubleshooting guide demonstrates this approach for delayed work: Debugging and troubleshooting DI.
Use runInInjectionContext for synchronous callbacks
Use runInInjectionContext when the callback is intentionally written to call inject(). The context exists only while the supplied function executes synchronously. It does not extend into a timer, a promise callback, or code after an await. Angular states this constraint in its runInInjectionContext API reference; check the documentation for the Angular version used by your project when relying on version-specific API details.
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Use TestBed’s context helper in tests
In a test, wrap the synchronous code that calls inject() in TestBed.runInInjectionContext(() => ...). This uses the testing environment’s injector context. See the TestBed API reference.
Make reusable helpers fail clearly
If a helper is designed to be called only from an injection context, call assertInInjectionContext(helperFunction) at its entry point. That checks the precondition and gives callers a clearer error when they invoke the helper from the wrong place. Angular documents the assertion in its injection-context guide.
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