I have recently started working with Angular and I am currently implementing an interceptor in my Angular project. In the code snippet below, the types for HttpRequest and HttpEvent are specified as any. However, I would like to specify the proper type for HttpRequest and HttpEvent. Can someone please assist me with this?
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {}
It is advisable to opt for unknown over any. The reason being that the type remains unknown during compilation and cannot truly be determined.
intercept(req: HttpRequest<unknown>, next: HttpHandler): Observable<HttpEvent<unknown>>
What is the reason for specifying the "appropriate type" in this scenario?
If you delve into the definitions of HttpRequest and HttpEvent, they are clearly outlined at this link and here.
The documentation indicates that the type parameter is denoted by T, representing a Generic Type.
This indicates the specific data type that needs to be retrieved.
For example, if you aim to fetch a collection of Users, your Request would appear as HttpRequest<User[]>. The definition of Users is project-specific rather than Angular-specific.
Understanding Generic Types
A Generic Type informs TypeScript that the actual type will be determined at Runtime, not during Compilation.
Compilation vs Runtime
During Compilation, all the checks and errors are analyzed before building the application. Runtime occurs when the application is actually run, such as in a browser environment.
At Runtime, T cannot exist as it must be replaced by a defined type like number, string, or a User-Defined Model.
Why is the type any used then?
All Interceptors adhere to the same Interface, and Angular relies on an Interceptor for server communication (link here).
The value represented by T signifies the data received from the Server, which is unknown beforehand.
This explains why any is utilized in this context.
Can the specific Type be defined in the Interceptor?
In theory, yes.
Does it function correctly? Uncertain.
Interceptors operate in sequence, hence modifying any to another type may lead to runtime issues.
Experimenting with this change might offer valuable insights.
Is this alteration advisable?
Probably not.
Interceptors handle various automated tasks like Logging and setting Auth-Headers. These operations should ideally be independent of response types.
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