Webpack Loader for MessageFormat

A loader that parses input JSON, YAML and Java .properties files consisting of messages as objects of JavaScript message functions with a matching structure, all during the build of your application.

This package was previously named messageformat-loader.


npm install --save-dev @messageformat/core @messageformat/loader

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

npm install @messageformat/runtime


After installation, you’ll need to add the loader to your Webpack config. Note the test value; you may want to customise the messages part to match whatever you’re actually using, in particular if a generic match like /\.yaml$/ would overlap with another loader.


module.exports = {
  module: {
    rules: [
        test: [/\bmessages\.(json|ya?ml)$/, /\.properties$/],
        type: 'javascript/auto', // required by Webpack for JSON files
        loader: '@messageformat/loader',
        options: { locale: ['en'] }

With that in place, you’ll be able to use your messages like this:


simple: 'A simple message.'
var: 'Message with {X}.'
plural: 'You have {N, plural, =0{no messages} one{1 message} other{# messages}}.'
select: '{GENDER, select, male{He has} female{She has} other{They have}} sent you a message.'
ordinal: 'The {N, selectordinal, one{1st} two{2nd} few{3rd} other{#th}} message.'


import messages from './messages.yaml';

messages.ordinal({ N: 1 });
// → 'The 1st message.'


In addition to the options accepted by @messageformat/core, the loader supports the following:

Option Type Default Description
convert boolean false Use @messageformat/convert to convert non-MessageFormat syntax and plural objects into MessageFormat. Use an object value to configure.
encoding 'auto'/'utf8'/ 'latin1' 'auto' File encoding. With 'auto', attempts to detect 'utf8', falling back to 'latin1'.
locale string[] ['en'] The CLDR language codes to pass to MessageFormat.
propKeyPath boolean true Parse dots . in .properties file keys as path separators, resulting in a multi-level message object.

As MessageFormat is often used to provide multi-language support, it’s important to include all of your supported locales in the options.locale value. For example, using locale: ['en', 'fr'] would allow for imports from foo.en.properties and foo.fr.properties 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.