[Typescript] Promise based delay function using async / await

Learn how to write a promise based delay function and then use it in 

async await

 to see how much it simplifies code over 

setTimeout

.

Lets say you want to call a function after 1s, 2s, 3s. You can use 

setTimeout

, or you can wrap it up into a simple delay function that works with async/await

const delay = (ms) => new Promise(res => setTimeout(res, ms));

const runAsync = async (cb) => { 
  await delay(100);
  cb('1s')
  await delay(1000);
  cb('2s')
  await delay(1000);
  cb('3s')
} 

runAsync((m) => { console.log(m)})      

or normal promise:

const delay = ms => new Promise(res => setTimeout(res, ms));

const runAsync = cb => {
  Promise.resolve()
    .then(() => {
      cb("1s");
      return delay(1000);
    })
    .then(() => {
      cb("2s");
      return delay(1000);
    })
    .then(() => {
      cb("3s");
      return delay(1000);
    });
};

runAsync(m => {
  console.log(m);
});