How to Add a Thousandths Place Comma (Every Three Digits) in JavaScript

Nick Scialli December 29, 2020🚀 1 minute read

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


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

// 1,000
// 1,000,000
// 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,');

// 1,000
// 1,000,000
// 1000

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

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Nick Scialli is a software engineer at the U.S. Digital Service.