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6.2.4 • Public • Published


Parse ICU MessageFormat pattern strings to a compact ast

npm Version JS Standard Style MIT License

Turns a ICU Message Format string:

`You have {
  numBananas, plural,
     =0 {no bananas}
    one {a banana}
  other {# bananas}
} for sale`

into a compact format-message ast:

[ "You have ", [ "numBananas", "plural", 0, {
     "=0": [ "no bananas" ],
    "one": [ "a banana" ],
  "other": [ [ '#' ], " bananas" ]
} ], " for sale." ]

Quick Examples

npm install format-message-parse --save

import parse from 'format-message-parse'
import interpret from 'format-message-interpret'

interpret('en', parse('Hello, {name}!'))({ name: 'Jane' })


parse(pattern: string, tokens?: ?Token[]): AST

Generate a compact array-based AST from an ICU MessageFormat string pattern. If an empty tokens array is passed in, it will be filled with found tokens.

This can throw a SyntaxError if the pattern is not valid. The offset property of the error lets you know how far into the pattern tokenization was able to go before the error. The tokens array will have all the found tokens up until the bad syntax.

Note that the only semantic validation done in parsing is ensuring that select, selectordinal, and plural include an other sub-message. It does not validate that a plural keyword applies to the locale, or that a style is supported by the type, or even that the type will be supported by the interpreter. Successful parsing is not a guarantee the final message will format as expected.


class SyntaxError extends Error {
  name: 'SyntaxError';
  message: string;
  expected: ?string;
  found: ?string;
  offset: number;
  line: number;
  column: number;


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

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