iteration/access pattern performance tests.

gistfile1.js

// test data
var array = [];
var dict = {};

var max = 1000000;

for(var i=0; i<max; i++)
{
    array[i] = i;
    dict[i] = i;
}

// tests
function testForInOnArray()
{
    for(var x in array)
    {
        array[x] = array[x] * 2;
    }
}

function testForInOnDict()
{
    for(var x in dict)
    {
        if(dict.hasOwnProperty(x))
            dict[x] = dict[x] * 2;
    }
}

function testForOnArray()
{
    for(var x=0; x < array.length; x++)
        array[x] = array[x] * 2;
}

function testForOnArrayWithCache()
{
    for(var x=0, l = array.length; x < l; x++)
        array[x] = array[x] * 2;
}

function testMapIterator()
{
    var iterator = map.entries();
    var entry;
    while ((entry = iterator.next()) !== null) {
        entry[1] = entry[1] * 2;
    }
}

function timeFunc(testFunc)
{
    var start = +new Date();
    testFunc();
    var end = +new Date();

    console.log("\ttime: " + (end - start));
}

console.log("array test. for in loop: ")
timeFunc(testForInOnArray);

console.log("array test. for loop: ")
timeFunc(testForOnArray);

console.log("array test. for loop with length cache: ")
timeFunc(testForOnArrayWithCache);

console.log("dict test. for in: ")
timeFunc(testForInOnDict);

array test. for in loop:
time: 339
array test. for loop:
time: 4
array test. for loop with length cache:
time: 3
dict test. for in:
time: 509