How to wait for service HTTP call to finish in component

Question

I have a service in which i'm sending HTTP request to the web api and waiting for response. I'm calling this service function in ngOnInit().

I want component to wait for service call to finish and depending upon the HTTP response i should redirect user.

Problem I call service function and component does not wait for it to finish and renders the page on screen then after 2 3 seconds it correctly redirects.. I don't want it to render..

web service

isTokenValid(token: any){

const body = token;
const headers = new Headers();
headers.append('Content-Type', 'application/json');
return this.http.post('http://'+this.web_url+':'+this.web_port+'/api/Authentication', body, {
  headers: headers
})
.map((data: Response) =>data.json());
}

service exampe code

verifyAccessToken(vaildDest: String, invalidDest: String, inverse:Boolean){
var localStorageObj = localStorage.getItem('currentUser');

if(localStorageObj == null){
  // no user details present in browser

  if(inverse) this.router.navigate([invalidDest]);
  return;

}

var currentUser = JSON.parse(localStorageObj);
var token = currentUser.AccessToken;
var email = currentUser.Email;
var isAccessTokenValid = false;
console.log(token);
var jsonStr = {
  "AccessToken": token,
  "Email": email
}
this.webService.isTokenValid(jsonStr)
.subscribe(
  data => {
    isAccessTokenValid = data["AccessValidation"]; 
    console.log("TOKEN SERVICE => isValid: "+isAccessTokenValid);
    // success connection

    if(!isAccessTokenValid){
      // access token is not valid now we will send refresh token
      console.log("=> Access token is not valid sending refresh token... ");


      if(inverse) this.router.navigate([invalidDest]);

    }
    else{
      // access token is valid so we can continue operation
      if(!inverse) this.router.navigate([invalidDest]);

    }

  },error => {
    console.log("Error while validating token");

  },
  () => {
    // 'onCompleted' callback.
    // No errors, route to new page here

  }
);
 }

Component code

constructor(private router: Router, private tokenService:TokenService) { }


ngOnInit() {
  this.tokenService.verifyAccessToken("","/welcome", true);

  // i want to stop it here and dont render current component until above call is finished
}

Answer 1

I suggest you to move the logic & the variables from service to component.

Service.ts :

function tryLogin(...put here your args): Observable<any> {
   return this.webService.isTokenValid(jsonStr);
   // Yep, just this. Usually services don't handle logic.
}

Component.ts :

this.tokenService.verifyAccessToken("","/welcome", true)
.subscribe(
  data => {
    isAccessTokenValid = data["AccessValidation"]; 
    console.log("TOKEN SERVICE => isValid: "+isAccessTokenValid);
    // success connection

    if(!isAccessTokenValid){
      // access token is not valid now we will send refresh token
      console.log("=> Access token is not valid sending refresh token... ");


      if(inverse) this.router.navigate([invalidDest]);

    }
    else{
      // access token is valid so we can continue operation
      if(!inverse) this.router.navigate([invalidDest]);

    }

  },error => {
    console.log("Error while validating token");

  },
  () => {
    // 'onCompleted' callback.
    // No errors, route to new page here

  }
);
 }

Anyway you can do something like that to prevent the page render before the subscription has finished:

Component example:

private canRender = false;

ngOnInit(): void {
   this.service.login(...)
   .subscribe( data => {
      //do Stuff
      this.canRender = true;
   });
}

related html to component :

<div ngIf="canRender">
   Content here will be render when you have the data you needed
   <!-- that when the line "this.canRender = true;" will be executed
</div>