icu-message-types

TypeScript utility types for extracting argument and tag types from ICU message strings.

Features

• Zero runtime overhead: Pure TypeScript types with no runtime impact
• Comprehensive format support: Supports all ICU message formats
• Extract message arguments: Extract argument types from ICU message strings
• Extract rich text tags: Extract tag names from ICU message strings

Installation

npm install icu-message-types

Note

Requires TypeScript >= 5.0

Quick Start

import type { ICUMessageArguments, ICUMessageTags } from 'icu-message-types';

// Extract argument types
type Args0 = ICUMessageArguments<'Hello, {firstName} {lastName}!'>;
// Result: { firstName: string | number | boolean; lastName: string | number | boolean }

type Args1 = ICUMessageArguments<`{theme, select,
  light {The interface will be bright}
  dark {The interface will be dark}
  other {The interface will use default colors}
}`>;
// Result: { theme: 'light' | 'dark' | ({} & string) | ({} & number) | boolean | null | undefined }

// Extract tag names
type Tags = ICUMessageTags<'Click <link>here</link> to continue'>;
// Result: 'link'

API Reference

ICUMessageArguments<T>

Extracts the argument types from an ICU message string.

Message Arguments

Format	TypeScript Type	Example
Unformatted	string | number | boolean | Date | null | undefined	{name}
number	number | `${number}` | null | undefined	{count, number, ...}
date	Date | number | `${number}` | null | undefined	{date, date, short}
time	Date | number | `${number}` | null | undefined	{time, time, medium}
plural	number | `${number}` | null | undefined	{count, plural, one {...} other {...}}
selectordinal	number | `${number}` | null | undefined	{position, selectordinal, one {#st} other {#th}}
select	'light' | 'dark' | {} & string | {} & number | boolean | null | undefined	{theme, select, light {...} dark {...} other {...}}

Additional Features

• Enhanced Value Types: Unformatted arguments accept string | number | boolean | Date | undefined | null
• String Number Support: Numeric formats accept both number and template literal `${number}`
• Comprehensive Select Matching: Select arguments with other clauses support string, number, boolean, null, and undefined
• Literal Type Transformation: Select keys are intelligently transformed (e.g., '123' becomes '123' | 123, 'true' becomes 'true' | true)
• Escaped content: Properly handles quoted/escaped text that shouldn't be parsed as arguments
• Nested messages: Supports complex nested structures
• Whitespace handling: Automatically strips whitespace and new lines for improved parsing

Basic String Arguments

type Args = ICUMessageArguments<'Hello, {name}!'>;
// Result: { name: string | number | boolean | Date | null | undefined }

type MultipleArgs = ICUMessageArguments<'Hello, {firstName} {lastName}!'>;
// Result: { firstName: string | number | boolean | Date | null | undefined; lastName: string | number | boolean | Date | null | undefined }

Number Arguments

type NumberArg = ICUMessageArguments<'I have {count, number} cats'>;
// Result: { count: number | `${number}` | null | undefined }

type CurrencyArg =
  ICUMessageArguments<'Price: {price, number, ::currency/USD}'>;
// Result: { price: number | `${number}` | null | undefined }

type PercentArg =
  ICUMessageArguments<'Progress: {progress, number, ::percent}'>;
// Result: { progress: number | `${number}` | null | undefined }

Date and Time Arguments

type DateArg = ICUMessageArguments<'Event date: {date, date, medium}'>;
// Result: { date: Date | number | `${number}` | null | undefined }

type TimeArg = ICUMessageArguments<'Meeting at {time, time, short}'>;
// Result: { time: Date | number | `${number}` | null | undefined }

Select Arguments

type SelectArg = ICUMessageArguments<`{theme, select,
  light {The interface will be bright}
  dark {The interface will be dark}
  other {The interface will use default colors}
}`>;
// Result: { theme: 'light' | 'dark' | ({} & string) | ({} & number) | boolean | null | undefined }

type SelectWithoutOther = ICUMessageArguments<`{status, select,
  active {Currently active}
  inactive {Currently inactive}
}`>;
// Result: { status: 'active' | 'inactive' }

Plural Arguments

type PluralArg = ICUMessageArguments<`{count, plural,
  =0 {No items}
  one {One item}
  other {# items}
}`>;
// Result: { count: number | `${number}` | null | undefined }

Selectordinal Arguments

type OrdinalArg = ICUMessageArguments<`{position, selectordinal,
  one {#st place}
  two {#nd place}
  few {#rd place}
  other {#th place}
}`>;
// Result: { position: number | `${number}` | null | undefined }

Nested Arguments

type NestedArgs = ICUMessageArguments<`{theme, select,
  dark {
    {count, plural,
      one {Dark mode shows one item}
      other {Dark mode shows # items}
    }
  }
  light {
    {count, plural,
      one {Light mode shows one item}
      other {Light mode shows # items}
    }
  }
  other {
    {count, plural,
      one {Default mode shows one item}
      other {Default mode shows # items}
    }
  }
}`>;
// Result: { theme: 'dark' | 'light' | ({} & string) | ({} & number) | boolean | null; count: number | `${number}` }

ICUMessageTags<T>

Extracts tag names from ICU message strings that contain HTML-like markup.

type SingleTag = ICUMessageTags<'Click <link>here</link>'>;
// Result: 'link'

type MultipleTags =
  ICUMessageTags<'Price is <bold>{price}</bold> with <link>discount</link>'>;
// Result: 'bold' | 'link'

type NestedTags = ICUMessageTags<'<wrapper><bold>text</bold></wrapper>'>;
// Result: 'wrapper' | 'bold'

type TagsWithAttributes =
  ICUMessageTags<'<a href="https://example.com">Link</a>'>;
// Result: 'a'

type NoTags = ICUMessageTags<'Plain text message'>;
// Result: never

Contributing

Contributions are welcome! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

Development

# Clone the repository
git clone https://github.com/offirgolan/icu-message-types.git
cd icu-message-types

# Install dependencies
npm install

# Run type tests
npm test

# Run linting
npm run lint

# Format code
npm run format

License

This project is licensed under the MIT License - see the LICENSE file for details.