promise.all.js

function all(promises) {
  return new Promise(function(resolve,reject) {
    var count = promises.length
    var result = []
    var checkDone = function() { 
      if (--count === 0) { 
        resolve(result) 
      }
    }
    
    promises.forEach(function(p, i) {
      p.then(function(x) { result[i] = x }, reject).then(checkDone)
    })
  })
}