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

Nick Scialli
December 29, 2020

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

Nick Scialli is a senior UI engineer at Microsoft.

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