async-parallel-and-sequential.js

console.clear();

(async () => {
  const list = ['one', 'two', 'three'];

  const doSlowly = msg => new Promise(resolve => {
    setTimeout(() => {
      resolve(`Processed ${msg}`);
    }, 100);
  });

  console.time('Processed sequentially in');
  
  const serialResults = [];
  
  for (const listItem of list) {
    const result = await doSlowly(listItem);
    serialResults.push(result);
  }
  console.timeEnd('Processed sequentially in');
  console.log('Serial results:', serialResults);


  console.time('Processed in parallel in');

  const parallelResults = await Promise.all(list.map(doSlowly));
  
  console.timeEnd('Processed in parallel in');
  console.log('Parallel results:', parallelResults);
})();