message-format

message-format

Intl.MessageFormat polyfill supporting ICU message format

Quick Start

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

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

var message = new MessageFormat('Hello { place }!', 'en-US');
var formatted = message.format({ place:'World' });

The library works great with tools like browserify and webpack for use in front-end code.

Note: message-format relies on Intl.NumberFormat and Intl.DateTimeFormat for formatting number, date, and time arguments. If you are in an environment missing these (like node <= 0.10, IE < 11, or Safari) you'll need to use a polyfill.

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.

message-format is intended as a polyfill for the yet to be standardized Intl.MessageFormat api. Since there is only a strawman proposal at this point, this library represents only one possible way the standard api could eventually work.

Loading locale data

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

Unsupported ICU Formats

ordinal, duration, and spellout arguments are supported by the parser, but will just toString(). These are not supported by Intl.NumberFormat. They require a lot of language-specific code, and would make the library undesireably large. For now, if you need these kinds of formats, you can pass them into the message pre-formatted, and refence them in the message pattern with a simple string placeholder ({ arg }).

Comparison to intl-messageformat

intl-messageformat is in many ways the inspiration for message-format. However, intl-messageformat deviates from the ICU standard in the way you escape special characters in the message pattern, and its pegjs generated parser is fairly large and not particularly speedy. message-format's primary goals are simplicity, compliance, and performance (both in size and speed).

If you prefer backslash escaping over the standard quote, you can enable it in the options:

new MessageFormat('message with \\{braces\\}', 'en-US', { escape:'\\' })

API

MessageFormat

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

new MessageFormat(pattern, [locales[, options]])

Construct a message format object

Parameters

• pattern is a properly formatted ICU Message Format pattern. A poorly formatted pattern will cause an Error to be thrown.
• locales is an optional string with a BCP 47 language tag, or an array of such strings.
• options is an optional object containing options that change the behavior of MessageFormat.
  • cache default true, if true cache the result of preparing the format function. The cache is shared across all instances of MessageFormat.
  • escape default ', if any other character, escape the single character following each escape character.

MessageFormat instances

message.format([args])

Format the message with the given arguments

Parameters

• args is an object containing the values to replace placeholders with. Required if the pattern contains placeholders.

Examples

Simple string placeholders

var message = new MessageFormat('Welcome back, {name}!');
message.format({ name:'Bob' }); // "Welcome back, Bob!"
message.format({ name:'Bill' }); // "Welcome back, Bill!"

Quote escaping rules

Escaping is a little weird in ICU Message Format.

1. '' is always '
2. ' begins an escaped string only if followed immediately by a syntax char ({}#)
3. ' ends an escaped string, unless it is doubled. See #1

The recommendation from ICU is to use the ASCII apostrophe (' U+0027) only for escaping syntax characters, and use the pretty single quote (’ U+2019) for actual apostrophes and single quotes in a message pattern.

var message = new MessageFormat('This isn\'\'t a \'{simple}\' \'string\'');
message.format(); // "This isn't a {simple} 'string'"

// double quotes or backticks (ES6) make it a little easier to read
message = new MessageFormat("This isn''t a '{simple}' 'string'");
message.format(); // "This isn't a {simple} 'string'"

number, date, and time placeholders

var message = new MessageFormat('You took {n,number} pictures since {d,date} {d,time}');
message.format({ n:4000, d:new Date() }); // "You took 4,000 pictures since Jan 1, 2015 9:33:04 AM"

message = new MessageFormat('{ n, number, percent }');
message.format({ n:0.1 }); // "10%"

message = new MessageFormat('{ shorty, date, short }');
message.format({ shorty:new Date() }); // "1/1/15"

Complex string with select and plural in ES6

import MessageFormat from 'message-format'

// using a template string for multiline, no interpolation
let message = new MessageFormat(`On { date, date, short } {name} ate {
  numBananas, plural,
       =0 {no bananas}
       =1 {a banana}
    other {# bananas}
  } {
  gender, select,
      male {at his house.}
    female {at her house.}
     other {at their house.}
  }`)

message.format({
  date: new Date(),
  name: 'Curious George',
  gender: 'male',
  numBananas: 27
}) // "On 1/1/15 Curious George ate 27 bananas at his house."

License

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