del.js

let r;
const runTasks = (...tasks) => Promise.all(tasks.map(t => t())).then(r => (r));

const tA = () => new Promise(r => setTimeout(() => r('A'), 1000));
const tB = () => new Promise(r => setTimeout(() => r('B'), 100));
const tC = () => new Promise(r => setTimeout(() => r('C'), 100));
runTasks(tA, tB, tC).then(re => {
  console.log(re);
});