Promise

Introducción

function doAsyncTask() {
  var promise = new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("Async Work Complete");
      if (error) {
        reject();
      } else {
        resolve();
      }
    }, 1000);
  });
  return promise;
}

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

let promise = Promise.resolve('done');
let promise = Promise.reject('fail');

Chaining

Promise.resolve(123)
    .then((res) => {
        console.log(res); // 123
        return 456;
    })
    .then((res) => {
        console.log(res); // 456
        return Promise.resolve(123); // Notice that we are returning a Promise
    })
    .then((res) => {
        console.log(res); // 123 : Notice that this `then` is called with the resolved value
        return 123;
    })


// Create a rejected promise
Promise.reject(new Error('something bad happened'))
    .then((res) => {
        console.log(res); // not called
        return 456;
    })
    .then((res) => {
        console.log(res); // not called
        return 123;
    })
    .then((res) => {
        console.log(res); // not called
        return 123;
    })
    .catch((err) => {
        console.log(err.message); // something bad happened
    });

Más Información

https://basarat.gitbooks.io/typescript/docs/promise.html
https://codecraft.tv/courses/angular/es6-typescript/promises/