JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = [];
for(var i=0;i<=1000000;i++){
    arr.push(i);
}

console.time("slowLoop"); //start the timer
for(var k=0,len = arr.length;k<len;k++){
    //do something
}
console.timeEnd('slowLoop');
console.time("fastLoop"); //start the timer
var j = arr.length;
while(j--){
    //do something;
}
console.timeEnd('fastLoop');


// Open browser console to see the benchmarks