I’ve been getting to know Intl.NumberFormat intimately lately. It is a pretty neat:

  • constructor for objects
  • to enable language sensitive number formatting
  • and this is JS standard built-in stuff, so I can run it in any empty browser console

The Intl object

…is the namespace for the ECMAScript Internationalization API, which provides language sensitive string comparison, number formatting, and date and time formatting.
 – MDN web docs on Intl

Nice, I see there’s a similar constructor for date and time formatting: Intl.DateTimeFormat. But for now, I want to format numbers to get control over decimal and thousands separators.


When I take it for a spin in the console, these two work as expected. It returns US style thousand separator comma and decimal point, while the Norwegian locale uses space and decimal comma.

// returns "123,456.789"
// returns "123 456,789"

What about default locale?

But I don’t want to hardcode the locale, I want to leave it to the user’s language preferences.

// returns the number “in the default locale and with default options”

But what is the default locale? Not at all straight forward! 🤯 There are so many different language settings. OS? Browser? Html lang attribute? MacOS system preferences has Language & Region, where I can define English as my preferred language, but Norway as the region. The advanced options under region can be edited, also per application. But default for Norway regarding numbers, is Grouping: space and Decimal: , (comma). This is exactly what I want (as a user) for reading numbers the way I’m used to reading them. But as a debugging developer, it’s a different story. Now I finally understand that:

👉 I have been getting 123,456.789 in the application I’m working on, because I have my OS set to English — and choosing Norwegian in the browser does not override that as I expected it would. To complicate things further for developers debugging i18n, it depends on the browser…

Limit the decimals with toFixed()

The code I’m working on has a method for calculating a percent using two values, and to limit the number of digits after the decimal separator, it uses toFixed(). Taking it this for a spin in an empty console to understand what this does:

((100 / 3) * 100).toFixed(2);
// returns "3333.33"
((100 / 2) * 100).toFixed(2);
// returns "5000.00" with the added zeros

This does exactly what I need. Most of the percentages have two digits behind the decimal separator. The added zeros, for the occasional instances of a value with only one digit or none, will make sure all numbers align and are scannable down the table column. 👍

Options argument for decimal

What happens when I format those percentages with my new best friend Intl.NumberFormat…?

// returns "5,000"    without added zeros :-(

But ha! I found out there are options! Sounds promising…

Intl.NumberFormat({ minimumFractionDigits: 2 }).format(5000.0);
// returns "5,000"       option is completely ignored

Intl.NumberFormat("en-US", { minimumFractionDigits: 2 }).format(5000.0);
// returns "5,000.00"    added zeros iz back :-)

Butbutbut I want this result without specifying the locale… Tried some versions with a space before the comma separating the options (SyntaxError!) empty strings with single quotes or double quotes (RangeError!). But yay, if I put an empty array in there, then it works:

Intl.NumberFormat([], { minimumFractionDigits: 2 }).format(5000.0);
// returns "5,000.00"