Web/JavaScript/Reference/Global objects/Array/toLocaleString

The toLocaleString() method returns a string representing the elements of the array. The elements are converted to Strings using their toLocaleString methods and these Strings are separated by a locale-specific String (such as a comma “,”).

Syntax

arr.toLocaleString([locales[, options]]);

Parameters

locales Optional: A string with a BCP 47 language tag, or an array of such strings. For the general form and interpretation of the locales argument, see the Intl page.
options Optional: An object with configuration properties, for numbers see Number.prototype.toLocaleString(), and for dates see Date.prototype.toLocaleString().

Return value

A string representing the elements of the array.

Polyfill

// https://tc39.github.io/ecma402/#sup-array.prototype.tolocalestring
if (!Array.prototype.toLocaleString) {
  Object.defineProperty(Array.prototype, 'toLocaleString', {
    value: function(locales, options) {
      // 1. Let O be ? ToObject(this value).
      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      var a = Object(this);

      // 2. Let len be ? ToLength(? Get(A, "length")).
      var len = a.length >>> 0;

      // 3. Let separator be the String value for the 
      //    list-separator String appropriate for the 
      //    host environment's current locale (this is 
      //    derived in an implementation-defined way).
      // NOTE: In this case, we will use a comma
      var separator = ',';

      // 4. If len is zero, return the empty String.
      if (len === 0) {
        return '';
      }

      // 5. Let firstElement be ? Get(A, "0").
      var firstElement = a[0];
      // 6. If firstElement is undefined or null, then
      //  a.Let R be the empty String.
      // 7. Else,
      //  a. Let R be ? 
      //     ToString(? 
      //       Invoke(
      //        firstElement, 
      //        "toLocaleString", 
      //        « locales, options »
      //       )
      //     )
      var r = firstElement == null ? 
        '' : firstElement.toLocaleString(locales, options);

      // 8. Let k be 1.
      var k = 1;

      // 9. Repeat, while k < len
      while (k < len) {
        // a. Let S be a String value produced by 
        //   concatenating R and separator.
        var s = r + separator;

        // b. Let nextElement be ? Get(A, ToString(k)).
        var nextElement = a[k];

        // c. If nextElement is undefined or null, then
        //   i. Let R be the empty String.
        // d. Else,
        //   i. Let R be ? 
        //     ToString(? 
        //       Invoke(
        //        nextElement, 
        //        "toLocaleString", 
        //        « locales, options »
        //       )
        //     )
        r = nextElement == null ? 
          '' : nextElement.toLocaleString(locales, options);

        // e. Let R be a String value produced by 
        //   concatenating S and R.
        r = s + r;

        // f. Increase k by 1.
        k++;
      }

      // 10. Return R.
      return r;
    }
  });
}

If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty, it's best not to polyfill Array.prototype methods at all, as you can't make them non-enumerable.

Examples

Using locales and options

The elements of the array are converted to strings using their toLocaleString methods.

Object: Object.prototype.toLocaleString()
Number: Number.prototype.toLocaleString()
Date: Date.prototype.toLocaleString()

Always display the currency for the strings and numbers in the prices array:

var prices = ['￥7', 500, 8123, 12]; 
prices.toLocaleString('ja-JP', { style: 'currency', currency: 'JPY' });

// "￥7,￥500,￥8,123,￥12"

For more examples, see also the Intl, NumberFormat, and DateTimeFormat pages.

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Array.prototype.toLocaleString' in that specification.
ECMAScript Internationalization API (ECMA-402)The definition of 'Array.prototype.toLocaleString' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`toLocaleString`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1	IE Full support 5.5	Opera Full support 4	Safari Full support 1	WebView Android Full support ≤37	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0	nodejs Full support 0.1.100
Optional `locales` parameter	Chrome Full support 24	Edge Full support 79	Firefox Full support 52	IE No support No	Opera Full support 15	Safari Full support 6.1	WebView Android Full support ≤37	Chrome Android Full support 25	Firefox Android No support No	Opera Android Full support 14	Safari iOS Full support 6.1	Samsung Internet Android Full support 2.0	nodejs Full support 13.0.0 Full support 13.0.0 Partial support 0.12 Notes' Notes' Before version 13.0.0, only the locale data for `en-US` is available by default. When other locales are specified, the function silently falls back to `en-US`. To make full ICU (locale) data available for versions prior to 13, see Node.js documentation on the `--with-intl` option and how to provide the data.
Optional `options` parameter	Chrome Full support 24	Edge Full support 79	Firefox Full support 52	IE No support No	Opera Full support 15	Safari Full support 6.1	WebView Android Full support ≤37	Chrome Android Full support 25	Firefox Android No support No	Opera Android Full support 14	Safari iOS Full support 6.1	Samsung Internet Android Full support 2.0	nodejs Full support 0.12

Legend

Full support: Full support
No support: No support
See implementation notes.': See implementation notes.