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.

[unicode messageformat 2.0]: https://unicode.org/reports/tr35/tr35-messageFormat.html
[messageformat working group]: https://github.com/unicode-org/message-format-wg
[ecma-402 intl.messageformat ]: https://github.com/tc39/proposal-intl-messageformat/
[ldml 48]: https://www.unicode.org/reports/tr35/tr35-76/tr35-messageFormat.html

``sh
npm install --save messageformat
`

`js
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

`js
import { parseMessage, stringifyMessage } from 'messageformat';
`

- MF2 data model validation and transformation tools

`js
import { validate, visit } from 'messageformat';
`

- Concreate Syntax Tree (CST) tools for MF2

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

- Utilities for building custom function handlers for MF2

`js
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.