References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript Intl.NumberFormat object

Object JavaScript All modern browsers Updated
Quick answer

The Intl.NumberFormat object formats numbers for a locale — currency, percentages, and proper thousands separators. new Intl.NumberFormat("en-US", { style: "currency", currency: "USD" }).format(1234.5) gives "$1,234.50". It's the correct way to display money, far better than manual string work or toFixed().

Overview

Intl.NumberFormat formats numbers the way humans in a given locale expect — with the right thousands separators, decimal marks, currency symbols and percentage signs. You create a formatter with a locale and options, then call .format(number) on it. It's part of the built-in Intl internationalization API, and it's the right tool for displaying money, percentages and large numbers.

The headline use is currency: new Intl.NumberFormat("en-US", { style: "currency", currency: "USD" }).format(1234.5) produces "$1,234.50" — correct symbol, grouping and decimals, all handled for you. Change the locale and currency and it adapts: "de-DE" with "EUR" gives "1.234,50 €". Other styles include "percent" (which also multiplies by 100), "decimal" and "unit".

Why not just use toFixed() and add a "$"? Because that breaks for other locales, large numbers and negative values, and ignores grouping. Intl.NumberFormat gets all of that right. One performance note: creating a formatter has a cost, so if you're formatting many numbers, create the formatter once and reuse it rather than constructing one per value. The convenience method number.toLocaleString() uses the same engine for one-off formatting.

Syntax

const fmt = new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD"
});
fmt.format(1234.5);    // "$1,234.50"

new Intl.NumberFormat("en-US", { style: "percent" }).format(0.25); // "25%"
(1234.5).toLocaleString("en-US");  // "1,234.5" (one-off)

Example

Live example 
<pre id="out" style="font:14px ui-monospace,monospace"></pre>
<script>
  const usd = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
  const eur = new Intl.NumberFormat('de-DE', { style: 'currency', currency: 'EUR' });

  document.getElementById('out').textContent =
    'USD: ' + usd.format(1234.5) + '\n' +
    'EUR: ' + eur.format(1234.5) + '\n' +
    'pct: ' + new Intl.NumberFormat('en-US', { style: 'percent' }).format(0.25);
</script>

Best practices

  • Use Intl.NumberFormat for currency and percentages, not manual strings or toFixed().
  • Create the formatter once and reuse it when formatting many numbers — construction is costly.
  • Pass an explicit locale and currency for predictable output.
  • Use number.toLocaleString() for a quick one-off format with the same engine.

Frequently asked questions

How do I format currency in JavaScript?
Use new Intl.NumberFormat("en-US", { style: "currency", currency: "USD" }).format(amount), which adds the symbol, separators and decimals correctly.
Why not just use toFixed() for money?
toFixed() doesn't add thousands separators, currency symbols or handle locales. Intl.NumberFormat does all of that.
How do I format a percentage?
Use { style: "percent" } — note it multiplies by 100, so pass 0.25 to get "25%".
How do I make number formatting fast?
Create one Intl.NumberFormat instance and reuse it for every value, instead of constructing a new one each time.
Intl.DateTimeFormat JSON