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Rollup Plugin for MessageFormat

Plugin for Rollup that lets you import JSON, YAML & .properties files containing ICU MessageFormat messages, turning them into message functions to use e.g. with @messageformat/react.


npm install --save-dev rollup-plugin-messageformat

If you’re intending to publish a library with external dependencies, you should also include the runtime as a dependency:

npm install @messageformat/runtime


With this config:

// rollup.config.js
import messageformat from 'rollup-plugin-messageformat'

export default {
  input: 'src/app.js',
  external: /^@messageformat\/runtime\b/,
  output: { format: 'es' },
  plugins: [messageformat({ locales: ['en', 'fr'] })]

And these source files:

# messages/fr.yaml
message_intro: |
  {count, plural,
    one {Votre message se trouve ici.}
    other {Vos # messages se trouvent ici.}
// src/app.js
import fr from '../messages/fr.yaml'

fr.message_intro({ count: 3 })
// 'Vos 3 messages se trouvent ici.'

You’ll get this output:

import { plural, number } from '@messageformat/runtime';
import { fr as fr$1 } from '@messageformat/runtime/lib/cardinals';

var fr = {
  message_intro: (d) => plural(d.count, 0, fr$1, {
    one: "Votre message se trouve ici.",
    other: "Vos " + number("fr", d.count, 0) + " messages se trouvent ici."
  }) + "\\n"

fr.message_intro({ count: 3 });
// 'Vos 3 messages se trouvent ici.'


In addition to the options accepted by @messageformat/core, the plugin supports the following. All are optional.

Option Type Default Description
exclude FilterPattern   Files to exclude. A valid minimatch pattern, or an array of such patterns.
include FilterPattern (see below) Files to include. A valid minimatch pattern, or an array of such patterns.
locales string[] ['en'] Define the message locale or locales using CLDR language codes. If given multiple valid locales, the first will be the default.
propKeyPath boolean true Parse dots . in .properties file keys as path separators, resulting in a multi-level message object.


By default, includes all .properties files and .json, .yaml & .yml files that include messages before the extension. If locales are defined, also matches messages[./_-]lc.ext where lc is the locale and ext one of the above extensions.

Examples of default matches:, messages.json, bar-messages.yaml, messages/en.json (if the en locale is explicitly set)


As MessageFormat is often used to provide multi-language support, it’s important to include all of your supported locales in the locales value. For example, using locales: ['en', 'fr'] would allow for imports from and to have their messages’ locale set correctly, based on the file name. Using a locale identifier as a key within the message file contents will also select that locale within it.

If locales has the special value '*', it will match all available locales. This may be useful if you want your messages to be completely determined by your data, but may provide surprising results if your input message object includes any 2-3 character keys that are not locale identifiers.