reduce and promises "$http" code example

Example: javascript reduce promises

const sum = await [
  Promise.resolve(1),
  Promise.resolve(1),
  Promise.resolve(1)
].reduce(async (previousPromise, itemPromise) => {
  const sum = await previousPromise;
  const item = await itemPromise;
  return sum + item;
}, Promise.resolve(0))

// sum === 3