Format a Number, Exactly Two in Length?

Question

I have an integer that is less then 100 and is printed to an HTML page with JavaScript. How do I format the integer so that it is exactly two digits long? For example:

Answer 1

I use regex to format my time such as

const str = '12:5'

const final = str.replace(/\d+/g, (match, offset, string) => match < 10 ? '0' + match : match)

output: 12:05