async & await

var apif1 = () => new Promise((resolve, reject) => {
  setTimeout(resolve, 1000, "one");
});
var apif2 = () => new Promise((resolve, reject) => {
  setTimeout(resolve, 2000, "two");
});

var apif3 = (values) => new Promise((resolve, reject) => {
  var flattened = values.reduce((acc, val) => acc.concat(val));
  setTimeout(resolve, 3000, flattened);
});

const combineTwo = async () => {
  const r1 = await apif1();
  const r2 = await apif2();
  const r3 = await apif3([r1, r2]);
  console.log(r3);
};

combineTwo();