Promise.all implementation

promise.all.js

function all(promises) {
  return new Promise((resolve, reject) => {
    if (!isIterable(promises)) {
      reject(new TypeError(`${promises} is not iterable`))
      return
    }
    const promisesArray = [...promises]
    if (promisesArray.length === 0) {
      resolve([])
      return
    }
    const results = []
    let numberOfResolved = 0
    promisesArray.forEach((promise, i) => {
      Promise.resolve(promise)
        .then((value) => {
          results[i] = value
          numberOfResolved++
          if (numberOfResolved === promisesArray.length) {
            resolve(results)
          }
        })
        .catch(reject)
    })
  })
}

function isIterable(item) {
  return typeof item[Symbol.iterator] === 'function'
}