Info

Dmitry Baranovskiy blew my mind with his dirtyCommas function, in which a very clever regular expression is used to format numbers with grouped thousands. Let’s see how it compares to other solutions.

Note that the functions benchmarked here were designed for use with positive integers only.

Preparation code

<script>
  function formatNumber1(number) {
   var comma = ',',
       string = Math.max(0, number).toFixed(0),
       length = string.length,
       end = /^\d{4,}$/.test(string) ? length % 3 : 0;
   return (end ? string.slice(0, end) + comma : '') + string.slice(end).replace(/(\d{3})(?=\d)/g, '$1' + comma);
  }
  
  function formatNumber2(number) {
   return Math.max(0, number).toFixed(0).replace(/(?=(?:\d{3})+$)(?!^)/g, ',');
  }
</script>

Test runner

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formatNumber1(100);
formatNumber1(1000);
formatNumber1(10000);
formatNumber1(100000);
formatNumber1(1000000);
formatNumber1(10000000);
formatNumber1(100000000);

formatNumber2(100);
formatNumber2(1000);
formatNumber2(10000);
formatNumber2(100000);
formatNumber2(1000000);
formatNumber2(10000000);
formatNumber2(100000000);

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Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

• Revision 1: published by Mathias Bynens on 3rd March 2011
• Revision 2: published on 23rd May 2011

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