Add commas to a number every 3 digits

formatNum.js

// add commas to a number every 3 digits

function formatNum1(num) {
    var STEP = 3;
    var DELIMITER = ',';
    var str = '' + num;
    var arr = str.split('');
    var len = arr.length;

    for(var i = len - STEP; i > 0; i -= STEP) {
        arr.splice(i, 0, DELIMITER);
    }

    return arr.join('');
}

function formatNum2(num) {
    return (num).toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

function formatNum3(num) {
    return (num).toLocaleString();
}


var TIMES = 1000000;
var num = 12345678;
var t1 = Date.now();

for(var i = 0; i < TIMES; i ++) {
    formatNum2(num);
}

var t2 = Date.now();

for(var j = 0; j < TIMES; j ++) {
    formatNum2(num);
}

var t3 = Date.now();

for(var k = 0; k < TIMES; k ++) {
    formatNum3(num);
}

var t4 = Date.now();

console.log(t2 - t1);
console.log(t3 - t2);
console.log(t4 - t3);