format-message

Write i18n messages inline. Transpile translations.

Quick Start

npm install format-message --save adds the library to node_modules. You can then use it as follows:

var formatMessage = require('format-message');

var message = formatMessage('Hello { place }!', { place:'World' });

You can configure your translations at runtime (typical for server-side use), or transpile your code for better performance in repeated use on the client.

format-message relies on the ECMAScript Internationalization API 1.0 (Intl) for formatting number, date, and time arguments. If you are in an environment missing these (like node <= 0.12, IE < 11, or Safari) you'll want to use a polyfill. Otherwise format-message falls back on toLocaleString methods, which are most likely just aliases for toString.

Format Overview

The ICU Message Format is a great format for user-visible strings, and includes simple placeholders, number and date placeholders, and selecting among submessages for gender and plural arguments. The format is used in apis in C++, PHP, and Java.

format-message provides a way to write your default (often English) messages as literals in your source, and then scrape out the default patterns and transpile your source with fast inline code for formatting the translated message patterns.

This relies on message-format for parsing and formatting ICU messages, and recast for transpiling the source code.

Supported ICU Formats

See message-format for supported ICU formats.

Quoting escaping rules

See the ICU site and message-format for details on how to escape special characters in your messages.

Loading locale data

format-message supports plurals for all CLDR languages. Locale-aware formatting of number, date, and time are delegated to the Intl apis, and select is the same across all locales. You don't need to load any extra files for particular locales for format-message itself.

API

formatMessage

var formatMessage = require('format-message')
// or
import formatMessage from 'format-message'

formatMessage(pattern[, args[, locales]])

Translate and format the message with the given pattern and arguments.

Parameters

• pattern is a properly formatted ICU Message Format pattern. A poorly formatted pattern will cause an Error to be thrown.
  • The pattern is used as a key into the translate function you provide in configuration, and is also used as the fallback if no translation is returned, or translate has not been configured
  • If pattern is not a string literal, the function cannot be transpiled at build time.
• args is an object containing the values to replace placeholders with. Required if the pattern contains placeholders.
• locales is an optional string with a BCP 47 language tag, or an array of such strings.
  • The locales are also passed into the translate function and indicate the desired destination language.
  • If locales is not a string literal, the function cannot be transpiled at build time.

formatMessage.setup

formatMessage.setup(options)

Configure formatMessage behavior for subsequent calls. This should be called before any code that uses formatMessage.

Parameters

• options is an object containing the following config values:
  • cache is whether message, number, and date formatters are cached. Defaults to true
  • locale is the default locale to use when no locale is passed to formatMessage. Defaults to "en".
  • translate(pattern, locales) is a function to translate messages. It should return the pattern translated for the specified locale.
    • pattern is the message pattern to translate.
    • locale is a string with a BCP 47 language tag, or an array of such strings.

internal apis

formatMessage.number, formatMessage.date, and formatMessage.time are used internally and are not intended for external use. Because these appear in the transpiled code, transpiling does not remove the need to properly define formatMessage through require or import.

Transpiled Messages

The examples provide sample transpiler output. This output is not meant to be 100% exact, but to give a general idea of what the transpiler does.

Simple messages with no placeholders

formatMessage('My Collections')

// transpiles to translated literal
"Minhas Coleções"

Simple string placeholders

formatMessage('Welcome, {name}!', { name: userName });

// messages with simple placeholders transpiles to concatenated strings
"Bem Vindo, " + userName + "!" // Bem Vindo, Bob!

Complex number, date, and time placeholders

formatMessage('{ n, number, percent }', { n:0.1 });

// transpiles to just the number call
formatMessage.number("en", 0.1, "percent") // "10%"


formatMessage('{ shorty, date, short }', { shorty:new Date() });

// transpiles to just the date call
formatMessage.date("en", new Date(), "short") // "1/1/15"


formatMessage('You took {n,number} pictures since {d,date} {d,time}', { n:4000, d:new Date() });

// transpiles to a function call, with the function defined at the top level
$$_you_took_n_number_pictures_123456({ n:4000, d:new Date() })
...
function $$_you_took_n_number_pictures_123456(args) {
  return "You took " + formatMessage.number("en", args["n"]) + " pictures since " + formatMessage.date("en", args["d"]) + " " + formatMessage.time("en", args["d"])
} // "You took 4,000 pictures since Jan 1, 2015 9:33:04 AM"

Complex string with select and plural in ES6

import formatMessage from 'format-message'

// using a template string for multiline, no interpolation
let formatMessage(`On { date, date, short } {name} ate {
  numBananas, plural,
       =0 {no bananas}
       =1 {a banana}
       =2 {a pair of bananas}
    other {# bananas}
  } {
  gender, select,
      male {at his house.}
    female {at her house.}
     other {at their house.}
  }`, {
  date: new Date(),
  name: 'Curious George',
  gender: 'male',
  numBananas: 27
})

// transpiles to a function call, with the function defined at the top level
$$_on_date_date_short_name_ate_123456({ n:4000, d:new Date() })
...
function $$_on_date_date_short_name_ate_123456(args) {
  return ...
}
// en-US: "On 1/1/15 Curious George ate 27 bananas at his house."

Current Optimizations

• Calls with no placeholders in the message become string literals.
• Calls with no plural, select, or selectordinal in the message, and an object literal with variables or literals for property values become concatentated strings and variables.

All other cases result in a function call, with the function declaration somewhere at the top level of the file.

CLI Tools

All of the command line tools will look for requireing or importing format-message in your source files to determine the local name of the formatMessage function. Then they will either check for problems, extract the original message patterns, or replace the call as follows:

format-message lint

Usage: format-message lint [options] [files...]

find message patterns in files and verify there are no obvious problems

Options:

-h, --help                  output usage information
-n, --function-name [name]  find function calls with this name [formatMessage]
--no-auto                   disables auto-detecting the function name from import or require calls
-k, --key-type [type]       derived key from source pattern literal|normalized|underscored|underscored_crc32 [underscored_crc32]
-t, --translations [path]   location of the JSON file with message translations, if specified, translations are also checked for errors
-f, --filename [filename]   filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]

Examples:

lint the src js files, with __ as the function name used instead of formatMessage

format-message lint -n __ src/**/*.js

lint the src js files and translations

format-message lint -t i18n/pt-BR.json src/**/*.js

format-message extract

Usage: format-message extract [options] [files...]

find and list all message patterns in files

Options:

-h, --help                  output usage information
-n, --function-name [name]  find function calls with this name [formatMessage]
--no-auto                   disables auto-detecting the function name from import or require calls
-k, --key-type [type]       derived key from source pattern (literal | normalized | underscored | underscored_crc32) [underscored_crc32]
-l, --locale [locale]       BCP 47 language tags specifying the source default locale [en]
-o, --out-file [out]        write messages JSON object to this file instead of to stdout

Examples:

extract patterns from src js files, dump json to stdout. This can be helpful to get familiar with how --key-type and --locale change the json output.

format-message extract src/**/*.js

extract patterns from stdin, dump to file.

someTranspiler src/*.js | format-message extract -o locales/en.json

format-message inline

Usage: format-message inline [options] [files...]

find and replace message pattern calls in files with translations

Options:

-h, --help                            output usage information
-n, --function-name [name]            find function calls with this name [formatMessage]
--no-auto                             disables auto-detecting the function name from import or require calls
-k, --key-type [type]                 derived key from source pattern (literal | normalized | underscored | underscored_crc32) [underscored_crc32]
-l, --locale [locale]                 BCP 47 language tags specifying the target locale [en]
-t, --translations [path]             location of the JSON file with message translations
-e, --missing-translation [behavior]  behavior when --translations is specified, but a translated pattern is missing (error | warning | ignore) [error]
-m, --missing-replacement [pattern]   pattern to inline when a translated pattern is missing, defaults to the source pattern
-i, --source-maps-inline              append sourceMappingURL comment to bottom of code
-s, --source-maps                     save source map alongside the compiled code
-f, --filename [filename]             filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]
-o, --out-file [out]                  compile all input files into a single file
-d, --out-dir [out]                   compile an input directory of modules into an output directory
-r, --root [path]                     remove root path for source filename in output directory [cwd]

Examples:

create locale-specific client bundles with source maps

format-message inline src/**/*.js -s -l de -t translations.json -o dist/bundle.de.js
format-message inline src/**/*.js -s -l en -t translations.json -o dist/bundle.en.js
format-message inline src/**/*.js -s -l es -t translations.json -o dist/bundle.es.js
format-message inline src/**/*.js -s -l pt -t translations.json -o dist/bundle.pt.js
...

inline without translating multiple files that used var __ = require('format-message')

format-message inline -d dist -r src -n __ src/*.js lib/*.js component/**/*.js

License

This software is free to use under the MIT license. See the LICENSE-MIT file for license text and copyright information.