Formatting - Add Leading Zero

add-leading-zero.js

/**
 * This gist is for Javascript beginners.
 * @author: Anthony Du Pont <[email protected]>
 * @site: https://www.twitter.com/JsGists
 *
 * You need sometimes to format you number and one of the common way to format them is to add a leading zero
 * to numbers less than 10. There is many ways of doing this so let me show you some of them.
 *
 * Example:
 * I have a number and I want to prepend a 0 to it if it's less than 10.
 **/

// Long way
let num = 3;
if (num < 10) {
  num = '0' + num; // Return `03`
}

// Short way
const numA = ('0' + 3).slice(-2); // Return `03`
const numB = ('0' + 10).slice(-2); // Return `10`

// Functional way
const numA = addLeadingZero(3); // Return `03`
const numB = addLeadingZero(10); // Return `10`

function addLeadingZero(number) {
  return ('0' + number).slice(-2);
}