how to access typescript class member from Javascript callback in one of class local method

Question

i have the folloing code:

export class AuthService {
  token: string;
  refreshToken: string;
  constructor(private router: Router) { }

  signinUser(username: string, password: string) {
      const user = new mylib.User(username, password);
      user.requestSessionToken(true, {
        onOk: function (result) {
          let tokenMap: any;
          tokenMap = result;
          this.token = tokenMap.sessionToken;
          this.refreshToken = tokenMap.refreshToken;
          mylib.Datastore.configureWithSessionToken(this.token);
          this.router.navigate(['/signup']);
        },
        onError: function (error) {
          console.error(error);
        }
      });
      console.log(this.token);
      console.log('signinUser Called!');
  }
}

mylib is Javascript library and this is not pointing to my object so this.token is not woking how can i access my class fields in Javascript block?

I think you will want to call user.token. this refers to the function signinUser since you are calling it outside of the object literal. Also, it appears that user.requestSessionToken is async, so you may need to use a callback or promise to wait until the function is finished before accessing this.token. — Wolfie
– Wolfie, Commented Aug 4, 2017 at 14:52
token is local member in AuthService class not in user — Abd
– Abd, Commented Aug 4, 2017 at 14:53
Please refer this doc - github.com/Microsoft/TypeScript/wiki/%27this%27-in-TypeScript — Yatin Patel
– Yatin Patel, Commented Aug 4, 2017 at 14:55

unional · Accepted Answer · 2017-08-04 16:48:53Z

Arrow function is the answer.

export class AuthService {
  token: string;
  refreshToken: string;
  constructor(private router: Router) { }

  signinUser(username: string, password: string) {
      const user = new mylib.User(username, password);
      user.requestSessionToken(true, {
        onOk: (result) => {
          let tokenMap: any;
          tokenMap = result;
          this.token = tokenMap.sessionToken;
          this.refreshToken = tokenMap.refreshToken;
          mylib.Datastore.configureWithSessionToken(this.token);
          this.router.navigate(['/signup']);
        },
        onError: (error) => {
          console.error(error);
        }
      });
      console.log(this.token);
      console.log('signinUser Called!');
  }
}

alternatively (old-school), you can use bind(): (function (result) { ... }).bind(this)

The reason is in the onOK callback, this is probably the user instance, not your class.

Always be careful on what is this when you are dealing with callbacks.

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