Please see: https://github.com/petkaantonov/bluebird/wiki/Optimization-killers#3-managing-arguments

safe_arguments.js

// should do the same as
// var args = Array.prototype.slice.call(arguments)
// without leaking arguments

var i = arguments.length
var args = new Array(i)
while (i-- !== 0) args[i] = arguments[i]

// should do the same as
// var args = Array.prototype.slice.call(arguments, 3);
// without leaking arguments

var i = arguments.length - 3
var args = []
if (i > 0) {
  args.length = i
  while (i-- !==0) args[i] = arguments[i + 3]
}