JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-2.1.0.debug.js"></script>

JavaScript

var bla = [];

for (var i =0; i < 1000000; i++)
{
  bla.push(i);        
}

var deb,fin;

var res = 0;

deb = new Date();

ko.utils.arrayForEach(bla, function(itm){
res = res+ itm;       
});

fin    = new Date();

alert(fin - deb + "    "   + res);

res=0;
deb = new Date();
var len = bla.length-1;
do
{    res = res+ bla[len];       

}while (len--);

    
   

fin    = new Date();

alert(fin - deb + "   " + res);