messageformat-parser

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

The generated parse(src, [options]) 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.

• strict – By default, the parsing applies a few relaxations to the ICU MessageFormat spec. Setting strict: true will disable these relaxations:

  • The argType of simpleArg formatting functions will be restricted to the set of number, date, time, spellout, ordinal, and duration, rather than accepting any lower-case identifier that does not start with a number.
  • The optional argStyle of simpleArg formatting functions will not be parsed as any other text, but instead as the spec requires: "In argStyleText, every single ASCII apostrophe begins and ends quoted literal text, and unquoted {curly braces} must occur in matched pairs."
  • 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 ('#'). In strict mode # will be parsed as a special character only 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, in which a single apostrophe only starts quoted literal text if it immediately precedes a curly brace {}, or a pound symbol # if inside a plural format. A literal apostrophe ' is represented by either a single ' or a doubled '' apostrophe character.

Installation

npm install messageformat-parser

Usage

> 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`.

For more example usage, please take a look at our test suite.

Structure

The output of parse() is a Token array:

type Token = string | Argument | Plural | Select | Function
 
type Argument = {
  type: 'argument',
  arg: Identifier
}
 
type Plural = {
  type: 'plural' | 'selectordinal',
  arg: Identifier,
  offset: number,
  cases: PluralCase[]
}
 
type Select = {
  type: 'select',
  arg: Identifier,
  cases: SelectCase[]
}
 
type Function = {
  type: 'function',
  arg: Identifier,
  key: Identifier,
  param: {
    tokens: options.strict ? [string] : (Token | Octothorpe)[]
  } | null
}
 
type PluralCase = {
  key: 'zero' | 'one' | 'two' | 'few' | 'many' | 'other' | '=0' | '=1' | '=2' | ...,
  tokens: (Token | Octothorpe)[]
}
 
type SelectCase = {
  key: Identifier,
  tokens: options.strict ? Token[] : (Token | Octothorpe)[]
}
 
type Octothorpe = {
  type: 'octothorpe'
}
 
type Identifier = string  // not containing whitespace or control characters

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Messageformat is an OpenJS Foundation project, and we follow its Code of Conduct.