promise example

async1.js

function doubleAfter2Seconds(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(x * 2);
    }, 2000);
  });
}

function addPromise(x){
  return new Promise(resolve => {
    doubleAfter2Seconds(10).then((a) => {
      doubleAfter2Seconds(20).then((b) => {
        doubleAfter2Seconds(30).then((c) => {
          resolve(x + a + b + c);
      	})
      })
    })
  });
}

addPromise(10).then((sum) => {
  console.log(sum);
});