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ES6 Promise.all for objects

7 Jan, 2017

function runInParallel (input) {
  let keys = []
  let promises = []
  for (let key in input) {
    keys.push(key)
    promises.push(input[key])
  }
  return Promise.all(promises).then((resolved) => {
    let output = {}
    for (let i = 0; i < resolved.length; i++) {
      output[keys[i]] = resolved[i]
    }
    return output
  })
}

Example:

runInParallel ({
  one: Promise.resolve('one'),
  two: Promise.resolve('two'),
}).then((obj) => {
  console.log(obj);
})

Gives:

{one: "one", two: "two"}

Be aware that if any promise fails, the Promise.all() call fails fast, so the catch() callback will only contain the one rejected promise, and won't wait for the other promises to settle.