const p1 = Promise.resolve(1);
const p2 = new Promise(resolve => resolve(2));
const p3 = new Promise(resolve => setTimeout(() => resolve(3), 0));
const p4 = Promise.reject(4).catch(err => err);

Promise.all([p1, p2, p3, p4])
  .then(values => {
    const result = values.reduce((acc, val) => {
      return acc + val;
    }, 0);
    console.log(result);
  })
  .catch(err => console.log('Error:', err));