How to use Promise in Typescript

let error = true;
function doAsyncTask() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (error) {
        reject('error'); // pass values
      } else {
        resolve('done'); // pass values
      }
    }, 1000);
  });
}

doAsyncTask().then(
  (val) => console.log(val),
  (err) => console.error(err)
);

Nested Promise

this.localStorage.clear().toPromise()
  .then((value1: boolean) => {
    console.log(value1);
    return this.localStorage.setItem(value.userName, value.token).toPromise();
  })
  .then((value2: boolean) => {
    console.log(value2);
  });

References
https://codecraft.tv/courses/angular/es6-typescript/promises/
https://stackoverflow.com/questions/40519484/promise-waterfall

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