Flatten an array in Javascript without recursion

flatten.js

'use strict'

var Benchmark = require('benchmark')
var suite = new Benchmark.Suite;

var list = [1, 2, 3, [[4]], [[[5]]], [6], [[7]]]

function flattenRecursive (list) {
  var flatList = []
  list.forEach(function (item) {
    if (item instanceof Array === true) {
      flatList = flatList.concat(flattenRecursive(item))
    } else {
      flatList.push(item)
    }
  })
  return flatList
}

function flatten (list) {
  var clonedList = list.slice(0)
  var flatList = []
  while (clonedList.length) {
    var item = clonedList.shift()
    if (item instanceof Array === true) {
      clonedList = item.concat(clonedList)
    } else {
      flatList.push(item)
    }
  }
  return flatList
}

suite.add('flattenRecursive', function() {
  flattenRecursive(list)
})
.add('flatten', function() {
  flatten(list)
})
.on('cycle', function(event) {
  console.log(String(event.target));
})
.on('complete', function() {
  console.log('Fastest is ' + this.filter('fastest').map('name'));
})
.run()