JS toLocaleString()

The toLocaleString() method converts a value to a string, using local formatting rules.

The toLocaleString() method is especially useful for formatting numbers, dates, arrays, currencies, and percentages for different countries.

The toLocaleString() Method

The toLocaleString() method is available for many JavaScript datatypes / objects:

• Numbers
• Dates
• Arrays
• BigInts

Example

let num = 1234567.89;

let text = num.toLocaleString();

Using Locales

You can specify a language and country code to format a value for a specific locale.

Example

let num = 1234567.89;

let us = num.toLocaleString("en-US");

let de = num.toLocaleString("de-DE");

let no = num.toLocaleString("no-NO");

Formatting Currency

With options, toLocaleString() can format numbers as currency.

Example

let price = 1299.95;

let dollars = price.toLocaleString("en-US",

{style:"currency", currency:"USD"});

let euros = price.toLocaleString("de-DE",

{style:"currency", currency:"EUR"});

let kroner = price.toLocaleString("no-NO",

{style:"currency", currency:"NOK"});

Formatting Percentages

The style:"percent" option formats a number as a percentage.

Example

let score = 0.875;

let result = score.toLocaleString("en-US", {style:"percent"});

Controlling Decimal Digits

You can control the number of decimal digits with minimumFractionDigits and maximumFractionDigits.

Example

let num = 3.14159;

let text = num.toLocaleString("en-US", {

  minimumFractionDigits: 2,

  maximumFractionDigits: 2

});

Note: The method name is toLocaleString(), not toLocalString(). The word locale means a language and country format, such as "en-US", "de-DE", or "no-NO".

Formatting Dates

Dates can also be formatted with toLocaleString().

Example

let date = new Date();

let text = date.toLocaleString("en-US");

Date Formatting Options

Many options can be used to control how dates are displayed.

Example

let date = new Date();

let text = date.toLocaleString("en-US", {

  weekday: "long",

  year: "numeric",

  month: "long",

  day: "numeric"

});

A Clever Use: Readable File Sizes

A clever use of toLocaleString() is to make file sizes easier to read.

Example

function fileSize(bytes) {

  if (bytes < 1024) return bytes + " bytes";

  if (bytes < 1024 * 1024) return (bytes / 1024).toLocaleString("en-US", {maximumFractionDigits: 1}) + " KB";

  return (bytes / 1024 / 1024).toLocaleString("en-US", {maximumFractionDigits: 1}) + " MB";

}

let size = 1536000;

let text = fileSize(size);

Arrays and toLocaleString()

For arrays, the toLocaleString() methods converts each array element.

Example

const dates = [

  new Date("2026-01-01"),

  new Date("2026-12-24")

];

let text = dates.toLocaleString("en-US");