messageformat

This library provides a formatter and other tools for Unicode MessageFormat 2.0 (MF2), the new standard for localization developed by the MessageFormat Working Group.

This includes a formatter that can be used as a polyfill for the proposed ECMA-402 Intl.MessageFormat formatter.

The API provided by this library is current as of the LDML 48 (October 2025) version of the MF2 specification.

npm install --save messageformat

import { MessageFormat } from 'messageformat';
import { DraftFunctions } from 'messageformat/functions';

const msg = 'Today is {$today :datetime dateStyle=medium}';
const mf = new MessageFormat('en', msg, { functions: DraftFunctions });

mf.format({ today: new Date('2022-02-02') });
// 'Today is Feb 2, 2022'

The library also provides a number of other tools and utilities for MF2, such as:

• MF2 data model conversion tools

  import { parseMessage, stringifyMessage } from 'messageformat';
  

• MF2 data model validation and transformation tools

  import { validate, visit } from 'messageformat';
  

• Concreate Syntax Tree (CST) tools for MF2

  import { parseCST, messageFromCST, stringifyCST } from 'messageformat/cst';
  

• Utilities for building custom function handlers for MF2

  import {
    DraftFunctions,
    asPositiveInteger,
    asString
  } from 'messageformat/functions';
  

In addition to supporting MF2 syntax, compilers and formatting function runtimes are also provided for ICU MessageFormat and Fluent messages:

• @messageformat/icu-messageformat-1
• @messageformat/fluent

For more information on the types and functions provided by this package, see the documentation site.

[!IMPORTANT] The v4 release of the messageformat package has an entirely different API compared to its earlier major releases, which were built on top of ICU MessageFormat, aka "MF1". For that, please see @messageformat/core instead.

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