A PEG.js parser for ICU MessageFormat strings – part of messageformat.js. Outputs an AST defined by parser.pegjs.

The generated parser function takes two parameters, first the string to be parsed, and a second optional parameter options, an object with the following possible keys:

• cardinal and ordinal – Arrays of valid plural categories for the current locale, used to validate plural and selectordinal keys. If these are missing or set to false, the full set of valid Unicode CLDR keys is used: 'zero', 'one', 'two', 'few', 'many', 'other'. To disable this check, pass in an empty array.

• strictFunctionParams – By default, function parameters are split on commas and trimmed, so the parameters in {x,fn, a, b } are parsed as ['a','b']. Setting strictFunctionParams to true will make the parser follow the ICU MessageFormat spec more closely, and result in a params array with a single element: [' a, b '].

• strictNumberSign – Inside a plural or selectordinal statement, a pound symbol (#) is replaced with the input number. By default, # is also parsed as a special character in nested statements too, and can be escaped using apostrophes ('#'). Setting strictNumberSign to true will make the parser follow the ICU MessageFormat spec more closely, and only parse # as a special character directly inside a plural or selectordinal statement. Outside those, # and '#' will be parsed as literal text.

The parser only supports the default DOUBLE_OPTIONAL apostrophe mode. A single apostrophe only starts quoted literal text if preceded by a curly brace ({}) or a pound symbol (#) inside a plural or selectordinal statement, depending on the value of strictNumberSign. Otherwise, it is a literal apostrophe. A double apostrophe is always a literal apostrophe.

npm install messageformat-parser

> var parse = require('messageformat-parser').parse; > parse('So {wow}.') [ 'So ', { type: 'argument', arg: 'wow' }, '.' ] > parse('Such { thing }. { count, selectordinal, one {First} two {Second}' + ' few {Third} other {#th} } word.') [ 'Such ', { type: 'argument', arg: 'thing' }, '. ', { type: 'selectordinal', arg: 'count', offset: 0, cases: [ { key: 'one', tokens: [ 'First' ] }, { key: 'two', tokens: [ 'Second' ] }, { key: 'few', tokens: [ 'Third' ] }, { key: 'other', tokens: [ { type: 'octothorpe' }, 'th' ] } ] }, ' word.' ] > parse('Many{type,select,plural{ numbers}selectordinal{ counting}' + 'select{ choices}other{ some {type}}}.') [ 'Many', { type: 'select', arg: 'type', cases: [ { key: 'plural', tokens: [ ' numbers' ] }, { key: 'selectordinal', tokens: [ ' counting' ] }, { key: 'select', tokens: [ ' choices' ] }, { key: 'other', tokens: [ ' some', { type: 'argument', arg: 'type' } ] } ] }, '.' ] > parse('{Such compliance') // SyntaxError: Expected ",", "}" or [ \t\n\r] but "c" found. > var msg = '{words, plural, zero{No words} one{One word} other{# words}}'; > var englishKeys = { cardinal: [ 'one', 'other' ], ordinal: [ 'one', 'two', 'few', 'other' ] }; > parse(msg) [ { type: 'plural', arg: 'words', offset: 0, cases: [ { key: 'zero', tokens: [ 'No words' ] }, { key: 'one', tokens: [ 'One word' ] }, { key: 'other', tokens: [ { type: 'octothorpe' }, ' words' ] } ] } ] > parse(msg, englishKeys) // Error: Invalid key `zero` for argument `words`. Valid plural keys for this // locale are `one`, `other`, and explicit keys like `=0`.

See the messageformat.js README for details.