[demo] async-await

async-await.js

const SEQUENCE = "sequence";
const PARALLEL = "parallel";

/**
 * wait
 *
 * @param s
 * @return {Promise}
 */
const wait = (s) => {
  return new Promise((resolve) => {
    setTimeout(resolve, s * 1000);
  });
};

/**
 * sequence
 *
 * @return {Promise.<string>}
 */
const sequence = async () => {
  await wait(2);
  await wait(3);
  return SEQUENCE;
};

/**
 * parallel
 *
 * @return {Promise.<string>}
 */
const parallel = async () => {
  const foo = wait(2);
  const bar = wait(3);

  await foo;
  await bar;

  return PARALLEL;
};

console.time(SEQUENCE);
sequence().then(console.timeEnd); // sequence: 5000ms

console.time(PARALLEL);
parallel().then(console.timeEnd); // parallel: 3000ms