打字稿推断类型而不使用显式类型变量进行回调

Question

I want to wrap rxjs subscribe's next callback with my function:

type Handler<T> = (value: T) => void;

export function withTryCatch<T>(callback?: Handler<T>): Handler<T> {

  return (value: T) => {
    try {
      callback?.(value);
    } catch(err) {
      // error handling
    }
  };
}

Problem with this example bellow is, that it does not automatically infer type from subscribe's next function. In this example, user type is stated as unknown . Only way how to make user desired type, is to explicitly set withTryCatch type variable T (see commented code below - withTryCatch<UserModel> ).

 store$
    .pipe(
      map(userSelector)
    )
    // .subscribe(withTryCatch<UserModel>((user) => {
    .subscribe(withTryCatch((user) => {
      // possible error code
    }));

Is there any way how to avoid using withTryCatch<UserModel> ?

Answer 1

This issue is separated from place where you use withTryCatch function, in that case it's rxjs subscribe method. When you just invoke it the generic T type parameter is unknown. When you call it with some type parameter then T is of course known. You could use Typescript inferring by typing user argument like here:

withTryCatch((user: UserModel) => {

});

You need to pass callback directly to subscribe to use Typescript inferring. Unfortunately it is impossible with that kind of wrapper function