BEFORE_APP_SERIALIZED is an injection token from Angular’s @angular/platform-server package. It lets an application register callbacks that run just before Angular’s server-rendering process serializes the current platform state to a string. Those callbacks may run synchronously or return a promise.
When does the hook run?
Angular calls the registered callbacks near the end of server rendering, immediately before renderApplication or renderModule renders the current platform state to a string. The hook is for work that needs to happen before that serialization step; it is not a general-purpose callback for every stage of application startup or rendering.
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Angular documents the token as a stable API. For version-specific behavior or migration questions, consult the API reference for the Angular version used by your application: Angular BEFORE_APP_SERIALIZED API reference.
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The token’s current type is InjectionToken<readonly (() => void | Promise<void>)[]>. A callback can finish synchronously by returning void, or represent asynchronous work by returning a Promise<void>. Angular’s source-level integration test demonstrates registering callbacks with multi providers, including a promise-based callback: Angular platform-server integration test.
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Here is the provider shape, adapted to illustrate the API:
{ provide: BEFORE_APP_SERIALIZED, useValue: () => { /* synchronous work */ }, multi: true }An asynchronous callback can return a promise:
{ provide: BEFORE_APP_SERIALIZED, useValue: () => doAsyncWork(), multi: true }Import the token from @angular/platform-server and register providers in the server-rendering configuration appropriate to your application. Check the documentation and declarations for your installed Angular version when adapting the example; the test shows the provider pattern, not a guarantee that every application should use this hook.
When should you use it?
Use the hook only when a particular task must finish immediately before server-rendered platform state is serialized. The key decision is whether that task is synchronous or asynchronous: return directly for synchronous work, or return its promise when completion must be represented asynchronously.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11The API definition establishes the timing and callback contract, but does not by itself recommend a specific production use case or spell out detailed error-handling guarantees. Base those decisions on the needs of your application and the documentation for its Angular version.
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