RXJS Tap function-CodePudding

I have this code can you please explain what does TAP function doing here?

 resend(id: number): void {
        this.orderService.resend(id).pipe(tap(() => { // TAP ()
            this.snackBarService.successMessage('table.resend_success_message');
          },
          error => this.snackBarService.errorMessage(),
        )).subscribe(() => {
          return this.getList(this.params);
        });
      }

CodePudding user response：

The comment of @Eliseo is correct but I will try to give you an example. In your case it's the same thing as doing this:

this.orderService.resend(id).subscribe(() => {
    this.snackBarService.successMessage('table.resend_success_message');
    return this.getList(this.params);
});

But this approach has some downside. If you want to subscribe to this.orderService.resend(id) from many places, you alway need to call this.snackBarService.successMessage. This is bad practice because we don't want to rewrite the same code multiple timse.

So a solution would be this:

resend$(id):Observable<any> { // this will return your list
    return this.orderService.resend(id).pipe(
        tap(() => this.snackBarService.successMessage('table.resend_success_message')),
        map(() => this.getList(this.params))
    );
});

test(){
    this.resend$(1).subscribe(
        myList => {
            // here you will have the list, no need to successMessage()
        }
    );
}

as you can see we could call this.resend$(1).subscribe() in multiple places and we don't need to call this.snackBarService.successMessage anymore