number formatting

number_format.js

function formatNumber(num) {
    num = num.toString();
    var result = '';
    for (var i = 1; i <= num.length; i++) {
        result = num[num.length - i] + result;
        if (i % 3 === 0 && i < num.length) {
            result = ',' + result;
        }
    }
    return result;
}

console.log(formatNumber(1));
console.log(formatNumber(22));
console.log(formatNumber(333));
console.log(formatNumber(4444));
console.log(formatNumber(55555));
console.log(formatNumber(666666));
console.log(formatNumber(7777777));