Javascript-承诺内在承诺

Question

Could somebody help me make a promise inside the promise? The code is

function getAccessToken(http: Http, router: Router, refreshTokenService: RefreshTokenService): Promise<string> {

let jwtHelper: JwtHelper = new JwtHelper();

let accessToken = localStorage.getItem('JWToken');

if (accessToken == '' || !accessToken || accessToken == undefined || accessToken == null) {
    router.navigate(['./admin/login']);
    return;
}

if (jwtHelper.isTokenExpired(accessToken)) {

    let waitPeriod = (!refreshTokenService.wait);

    refreshTokenService.wait = true;

    return new Promise((resolve, reject) => {

        if (waitPeriod) {
            refreshTokenService.refreshToken(accessToken).subscribe((res: any) => {
                res = res.json();

                if (res.token) {
                    localStorage.setItem('JWToken', res.token);
                    resolve(res.token);
                    refreshTokenService.wait = false;
                } else {
                    localStorage.removeItem('JWToken');
                    router.navigate(['./admin/login']);
                }

            });
        } else {
            let interval = setInterval(function () {
                if(refreshTokenService.wait == false) {
                    resolve(localStorage.getItem('JWToken'));
                    clearInterval(interval);
                }
            }, 500);
        }

    });
} else {
    return Promise.resolve(accessToken);
}
}

As you can see, i use a variable refreshTokenService.wait and a setInterval to check periodicaly if the value is changed. But i think the best aproach will be a Promise inside the promise.

Answer 1

You can just keep the current running promise as a class variable and return it to all other clients. as soon as promise resolved - set it to null.

class Test {
 getData() {
   if(!this.request) {
     this.request = new Promise((res)=> {
       console.log('start request')
       setTimeout(()=>res('token' + new Date()), 1000);
     }).then(token=> {
      this.request = null;
      return token;
    });
   }
   return this.request;
 }
}

let t = new Test();

// all these clients get the same result
t.getData().then(x=>console.log(x));
t.getData().then(x=>console.log(x));
t.getData().then(x=>console.log(x));

// all these clients get the another result
setTimeout(()=> {
 t.getData().then(x=>console.log(x));
 t.getData().then(x=>console.log(x));
 t.getData().then(x=>console.log(x));
}, 3000);