batch-promise.js

function(promises, { seq, progress } = {}) {
  const results = new Array(promises.length).fill(undefined)

  let count = 0

  return new Promise(async (resolve, reject) => {
    async function runPromise(promise, i) {
      results[i] = await promise
      count += 1

      if(progress)
        progress((count / promises.length).toFixed(2))

      if(count === promises.length)
        resolve(results)
    }

    if(seq)
      for(let i = 0; i < promises.length; i++)
        await runPromise(promises[i], i)
    else
      promises.forEach(runPromise)
  })
}