Executing of immediate navigation in async/await functions by the router

In my component A, there is an async method abc(). Within this method, I await another async method xyz() from service X. This xyz() method contains additional await calls (which need to be executed sequentially and use the response for subsequent requests). In certain scenarios where specific calls return negative results, I want to redirect the user to one of two pages (for now, let's assume it's just one page). I am currently using router.navigate(['/error']), but the redirection is not functioning as intended. I expect it to halt further code execution and immediately redirect the user.

x.service.ts

async ngOnInit() {
   await this.abc();
}

async abc(): Promise<any> {
   await this.serviceX.xyz();

   // The following calls still proceed even if the navigation line in the xyz() method is accessed
   await this.service3.magicMethod();
   await this.service4.anotherMethod();
}

a.component.ts

async xyz(): Promise<any> {
   const result = await this.service1.getData(); 
   if (result !== 'OK') {
      this.router.navigate(['/error']);
   }

   const userAnswer = await this.service2.userSelection();
   if (userAnswer !== 'OK') {
      this.router.navigate(['/error']);
   }
}

Both service1 and service2 consist of async functions where HTTP responses are awaited using toPromise(). For example:

async getData(): Promise<SomeResponse> { // or userSelection()
   const response = await this.wrapperService.getHttpResponse().toPromise();
   console.log(response);
   return response as SomeResponse;
}

Answer №1

If you want the processing to halt, make sure to explicitly instruct it to do so. The function router.navigate will keep running unless instructed otherwise.

In this scenario, it appears that routing is being handled within the service, which introduces UI-related concerns into the service layer. It would be better to refactor the service method to return a result indicating success or failure. Subsequently, the component can decide whether to navigate or proceed with further processing.

service.ts

async xyz(): Promise<boolean> {
   const result = await this.service1.getData(); // 
   if (result !== 'OK') {
       // stop processing
      return false;
   }

   const userAnswer = await this.service2.userSelection();
   if (userAnswer !== 'OK') {
      // stop processing
      return false;
   }

   return true;
}

component.ts

async ngOnInit() {
   await this.abc();
}

async abc(): Promise<any> {
   const success = await this.serviceX.xyz();
   if (!success) {
     this.router.navigate(['/error']);
     // no further processing
     return;
   }

   await this.service3.magicMethod();
   await this.service4.anotherMethod();
}

I have included return; statements after each call to router.navigate to prevent further processing.

If your service needs to return more than true/false, consider returning an error message or an object. However, for demonstration purposes, a boolean suffices.

EDIT:

If you truly wish to handle routing within the service, go ahead and do so. Just remember to follow the pattern of returning a success result, incorporating navigation before each return false; statement.

EDIT 2:

As mentioned in the comments, my intention is not to dictate your design choices, but rather offer a solution pattern. While there may be additional overhead in returning an error result and mapping it to a path, I personally prefer this approach for clarity over mixing routing with data calls - aiming to avoid "spaghetti code."

The provided example demonstrates how to separate service calls from routing. It serves as a pattern suggestion rather than finalized code, but hopefully sparks some ideas on cleaner design approaches. I don't mind putting in extra work for a more organized structure.

service.ts

export enum XyzError = { ErrorA = 1, ErrorB = 2 }

async xyz(): Promise<XyzReason> {
   const result = await this.service1.getData(); // 
   if (result !== 'OK') {
       return XyzReason.ErrorA;
   }

   const userAnswer = await this.service2.userSelection();
   if (userAnswer !== 'OK') {
      return XyzReason.ErrorB;
   }

   return null;
}

component.ts

async abc(): Promise<any> {
   const result: XyzReason = await this.serviceX.xyz();
   switch (result)  {
     case XyzReason.ErrorA:
       this.router.navigateByUrl('/errora');
       return;
     case XyzReason.ErrorB:
       this.router.navigateByUrl('/errorb');
       return;
   }

   await this.service3.magicMethod();
   await this.service4.anotherMethod();
}

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