[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();
  cb('1s')
  await delay();
  cb('2s')
  await delay();
  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);
});