README.md

@phensley/messageformat

Compact and extensible ICU message formatter with built-in support for plural, select, and selectordinal. Also supports plural calculations using arbitrary precision decimal numbers.

Installation

NPM:

npm install --save @phensley/messageformat

Yarn:

yarn add @phensley/messageformat

Examples

Setup

The package allows you to wire up the different types how you want. Things are broken out so that parsing can be done separately from evaluation.

Parsing can be done at build time -- read a YAML file, parse messages and embed them into a YAML/JSON file, or embed them into code, for faster runtime message evaluation.

Custom formatting and argument conversion functions can be defined and plugged into the framework.

import { pluralRules } from '@phensley/plurals';
import {
  buildMessageMatcher,
  parseMessagePattern,
  DefaultMessageArgConverter,
  MessageArg,
  MessageEngine,
  MessageFormatter,
  MessageNamedArgs
} from '@phensley/messageformat';

const FORMATTERS = {
  foo: (args: MessageArg[], options: string[]) =>
    options[0] === 'upper' ? args[0].toUpperCase() : args[0].toLowerCase()
};

const FORMATTER_NAMES = Object.keys(FORMATTERS);

const MATCHER = buildMessageMatcher(FORMATTER_NAMES);

const CONVERTER = new DefaultMessageArgConverter();

const parse = (message: string) => parseMessagePattern(message, MATCHER);

const dump = (message: string) => console.log(JSON.stringify(parse(message)));

const plurals = (language: string, region?: string) =>
  pluralRules.get(language, region);

const format = (
  message: string,
  positional: MessageArg[],
  named: MessageNamedArgs = {}
) => {
  const engine = new MessageEngine(
    plurals('en'),
    CONVERTER,
    FORMATTERS,
    parse(message)
  );
  console.log(engine.evaluate(positional, named));
};

let msg: string;

Example 1 - message parsing (cache for repeated use)

Messages can be pre-parsed and embedded into source code, JSON, or YAML files, or parsed and cached at runtime.

dump('{0 select, male {his} female {her} other {their}} {item}');

[4,[[3,[0],[["male",[0,"his"]],["female",[0,"her"]],["other",[0,"their"]]]],[0," "],[1,"item"]]]

dump('{word} uppercase = {word foo upper} lowercase = {word foo lower}');

[4,[[1,"word"],[0," uppercase = "],[6,"foo",["word"],["upper"]],[0," lowercase = "],[6,"foo",["word"],["lower"]]]]

Example 2 - MessageFormatter class

If you don't need to embed parsed messages into source code, the MessageFormatter can parse and cache messages at runtime. Internally it uses a least-recently-used cache whose size can be configured. There is no need for the elaborate setup in the first example.

const rules = plurals('en');
const formatter = new MessageFormatter({
  plurals: rules,
  formatters: FORMATTERS,
  cacheSize: 100
});
msg = '{0 select, male {his} female {her} other {their}} {item}';
console.log(formatter.format(msg, ['female'], { item: 'parka' }));

her parka

Example 3 - plural cardinals

msg =
  '{count, plural, offset:1 =0 {Be the first to like this} =1 {You liked this} ' +
  'one {You and someone else liked this} other {You and # others liked this}}';

format(msg, [], { count: 0 });
format(msg, [], { count: 1 });
format(msg, [], { count: 2 });
format(msg, [], { count: 3 });

Be the first to like this
You liked this
You and someone else liked this
You and 2 others liked this

Example 4 - select

msg = 'Get {0, select, male {his} female {her} other {their}} {item}';

format(msg, ['they'], { item: 'coat' });
format(msg, ['female'], { item: 'jacket' });
format(msg, ['male'], { item: 'parka' });

Get their coat
Get her jacket
Get his parka

Example 5 - plural ordinals and select

msg =
  '{name} {tied select true {tied for} other {came in}} {place selectordinal one {#st} ' +
  'two {#nd} few {#rd} other {#th}} place';

const racers = [
  { name: 'Lisa', place: 1 },
  { name: 'Bob', place: 2 },
  { name: 'Betty', place: 3 },
  { name: 'Frank', place: 4, tied: true },
  { name: 'George', place: 4, tied: true },
  { name: 'Larry', place: 5 }
];

for (const racer of racers) {
  format(msg, [], racer);
}

Lisa came in 1st place
Bob came in 2nd place
Betty came in 3rd place
Frank tied for 4th place
George tied for 4th place
Larry came in 5th place

Example 6 - custom formatter

msg = '{word} uppercase = {word foo upper} lowercase = {word foo lower}';

const WORDS = ['Computer', 'Science', 'Mathematics'];

for (const word of WORDS) {
  format(msg, [], { word });
}

Computer uppercase = COMPUTER lowercase = computer
Science uppercase = SCIENCE lowercase = science
Mathematics uppercase = MATHEMATICS lowercase = mathematics