Start downloading files simultaneously, but display them in order

promise-chain.js

const files = [fetch('file1'), fetch('file2'), fetch('file3')];

let chain = Promise.resolve();

for (const file of files) {
  chain = chain
    .then(() => {
      return file;
    })
    .then(file => console.log(file));
}

function fetch(file) {
  const delay = Math.random() * 3000;
  return new Promise(resolve => {
    setTimeout(() => {
      console.log(`${file} received`);
      resolve(file);
    }, delay);
  });
}