Let’s do some basic number formatting for large numbers in JavaScript. If you’re here, you probably to be able to make the following conversions:

• 1000 -> 1,000
• 1000000 -> 1,000,000
• 100 -> 100

You’re in luck: there are a couple fairly simple ways to do this in JavaScript

toLocaleString

One simple option is the built-in toLocaleString string method. It goes something like this:

(1000).toLocaleString('en-US');
// 1,000
(1000000).toLocaleString('en-US');
// 1,000,000
(100).toLocaleString('en-US');
// 1000

Regular Expressions

Another option is to use a Regular Expression. If our input is a number, we’ll want to make sure to covert it to a string before applying the regex.

function addCommas(num) {
  return num.toString().replace(/(\d)(?=(\d\d\d)+(?!\d))/g, '$1,');
}

addCommas(1000);
// 1,000
addCommas(1000000);
// 1,000,000
addCommas(100);
// 1000

And that’s it! A couple fairly straightforward ways to add commas to your large numbers.