loop.bench.js

function bench (lmbd) {
  var     i = 0,
      start = new Date().getTime()
  while (i!=10000) {
    lmbd()
    ++i
  }
  return new Date().getTime() - start
}

var arr = new Array(1000)
for (var i = 0, il = arr.length; i < il; i++) {
  arr[i] = i;
}

console.log("Warmup : "+bench(function() {
        var sum = 0
        arr.forEach( function(e) {
          sum += e  
        })
      }))
console.log("length cached : "+bench(function() {
        var sum = 0
        for (var i = 0, len = arr.length; i < len; i++) {
          sum += arr[i]
        }
      }))

console.log("length not cached : "+bench(function() {
        var sum = 0
        for (var i = 0; i < arr.length; i++) {
          sum += arr[i]
        }
      }))

console.log("length not cached comp w/ != : "+bench(function() {
        var sum = 0
        for (var i = 0; i != arr.length; i++) {
          sum += arr[i]
        }
      }))
console.log("length not cached preinc : "+bench(function() {
        var sum = 0
        for (var i = 0; i < arr.length; ++i) {
          sum += arr[i]
        }
      }))
console.log("forEach : "+bench(function() {
        var sum = 0
        arr.forEach( function(e) {
          sum += e  
        })
      }))