@lingui/macro - Reference

@lingui/macro package provides babel macros which transforms template literals and JSX into messages in ICU MessageFormat.

Overview

All macros are transformed to <Trans> component from @lingui/react.

Here are few examples of JS macros. These macros create a message descriptor with a message in MessageFormat syntax:

JS Macro Result
t`Refresh inbox`
/*i18n*/{
  id: "Refresh inbox"
}
t("msg.refresh")`Refresh inbox`
/*i18n*/{
  id: "msg.refresh",
  defaults: "Refresh inbox"
}
t`Attachment ${name} saved`
/*i18n*/{
  id: "Attachment {name} saved",
  values: { name }
}
plural({
  value: count,
  one: "Message",
  other: "Messages"
})
/*i18n*/{
  id: "{count, plural, one {Message} other {Messages}}",
  values: { count }
}
t`Today is ${date(today)}`
/*i18n*/{
  id: "Today is {today, date}",
  values: { today }
}

Following examples are the same messages above but written using JSX macros. As above, macros create a message in MessageFormat syntax, but this time the result in <Trans> component:

JSX Macro Result
<Trans>Refresh inbox</Trans> <Trans id="Refresh inbox" />
<Trans id="msg.refresh">Refresh inbox</Trans> <Trans id="msg.refresh" defaults="Refresh inbox" />
<Trans>Attachment {name} saved</Trans> <Trans id="Attachment {name} saved" />
<Plural value={count} one="Message" other="Messages" /> <Trans id="{count, plural, one {Message} other {Messages}}" />
<Trans>Today is <DateFormat value={today} /></Trans> <Trans id="Today is {today, date}" />

Generated message is used as a message ID in catalog, but can be overriden by custom ID. Generated message is guaranteed to be syntactically valid.

Installation

Babel macros require babel-plugin-macros to work. If you use a framework (for example GatsbyJS, Create React App >2.0) you might already have macros enabled. Otherwise install it as any other Babel plugin:

  1. Install babel-plugin-macros as a development dependency:

    npm install --save-dev babel-plugin-macros
    # yarn add --dev babel-plugin-macros
    
  2. Add macros to the top of plugins section in your Babel config.

    {
       "plugins": [
          "macros"
       ]
    }
    

Once you project has macros enabled, install @lingui/macro as a development dependency:

npm install --save-dev @lingui/macro
# yarn add --dev @lingui/macro

Usage

JS macros

These macros can be used in any context (e.g. outside JSX) and are intended to work in combination with i18n._ method. All JS macros are transformed into a Message Descriptor which is an object with message ID, default message and other parameters. i18n._ accepts message descriptors and performs translation and formatting:

type MessageDescriptor = {
   id: String,
   defaults?: String,
   values?: Object,
   formats?: Object,
}

id is message ID and the only required parameter. id and defaults are extracted to message catalog. Only id, values, and formats are used at runtime, all other attributes are removed from production code for size optimization.

Description

All JS macros can have a description. Description is added using i18n comment in front of the macro:

/*i18n: Description*/t`Message`

// ↓ ↓ ↓ ↓ ↓ ↓
/*i18n: Description*/{
  id: 'Message'
}

Description is extracted to message catalog as a help text for translators.

t

t

The most common macro for messages. It transforms tagged template literal into message in ICU MessageFormat. It’s allowed to use other i18n macros as variables.

import { setupI18n } from "@lingui/core"
import { t } from "@lingui/macro"

const i18n = setupI18n()

// Static Message
const static = i18n._(t`Static Message`)
// ↓ ↓ ↓ ↓ ↓ ↓
// const static = i18n._(/*i18n*/{
//   id: 'Static',
// })

// My name is {name}
const vars = i18n._(t`My name is ${name}`)

// Macros can be nested, date is macro for date formatting
const date = i18n._(t`Today is ${date(name)}`)

Call macro with a custom message ID to override auto-generated one.

const id = i18n._(t('msg.id')`My name is ${name}`)

plural

plural

plural macro is used for pluralization, e.g: messages which has different form based on counter. It accepts an object with required key value which determines the plural form. The only required plural form is a catch-all other. Other forms depends on source language you’re using (e.g: English has one and other plural forms).

import { setupI18n } from "@lingui/core"
import { plural } from "@lingui/macro"

const i18n = setupI18n()

const msg = i18n._(plural({
   value: count,
   one: "# Book",
   other: "# Books"
}))

// t macro isn't required for nested messages,
// template strings are transformed automatically.
const vars = i18n._(plural({
   value: count,
   one: `${name} has # friend`,
   other: `${name} has # friends`
}))

// Example of pluralization using two counters
const double = i18n._(plural({
   value: numBooks,
   one: plural({
      value: numArticles,
      one: `1 book and 1 article`,
      other: `1 book and ${numArticles} articles`,
   }),
   other: plural({
      value: numArticles,
      one: `${numBooks} books and 1 article`,
      other: `${numBooks} books and ${numArticles} articles`,
   }),
}))

Call macro with a string as a first argument to override auto-generated message ID.

// Override auto-generated message ID
const id = i18n._(plural("msg.id", {
   value: count,
   one: "# Book",
   other: "# Books"
}))

date

date

This macro marks variable as a date which is formatted using Intl.DateTimeFormat.

First parameter is a value to be formatted.

Second argument (optional) specifies date format.

import { setupI18n } from "@lingui/core"
import { t, date } from "@lingui/macro"

const i18n = setupI18n()

const today = new Date()
const msg = i18n._(t`Today is ${date(today)}.`)

number

number

This macro marks variable as a number which is formatted using Intl.NumberFormat.

First parameter is a value to be formatted.

Second argument (optional) specifies number format.

import { setupI18n } from "@lingui/core"
import { t, number } from "@lingui/macro"

const i18n = setupI18n()

const msg = i18n._(t`There were ${number(10000)} people.`)
const percent = i18n._(t`Interest rate is ${number(0.05, "percent")}.`)

JSX Macros

Common props

All macros share following props:

id

Each message in catalog is identified by message ID.

While all macros use generated message as the ID, it’s possible to override it. In such case, generated message is used as a default translation.

import { Trans } from "@lingui/macro"

<Trans id="message.attachment_saved">Attachment {name} saved.</Trans>

// ↓ ↓ ↓ ↓ ↓ ↓
// <Trans id="message.attachment_saved" defaults="Attachment {name} saved." />
description

Description of the message which is extracted to message catalogs as a help text for translators. It’s removed from production code.

render

Custom component to render translation into. This prop is directly passed to <Trans> component from @lingui/react. See rendering of translations for more info.

Trans

Trans
Props:
  • id (string) – Custom message ID

<Trans> is the basic macro for static messages, messages with variables, but also for messages with inline markup.

import { Trans } from "@lingui/macro"

<Trans>Refresh inbox</Trans>;
// ↓ ↓ ↓ ↓ ↓ ↓
// <Trans id="Refresh inbox" />

<Trans id="message.attachment_saved">Attachment {name} saved.</Trans>
// ↓ ↓ ↓ ↓ ↓ ↓
// <Trans id="message.attachment_saved" defaults="Attachment {name} saved." />

This macro is especially useful when message contains inline markup.

import { Trans } from "@lingui/macro"

<Trans>Read the <a href="/docs">docs</a>.</Trans>;
// ↓ ↓ ↓ ↓ ↓ ↓
// <Trans id="Read the <0>docs</0>." components={[<a href="/docs" />]} />

Components and HTML tags are replaced with dummy indexed tags (<0></0>) which has several advatanges:

  • both custom React components and built-in HTML tags are supported
  • change of component props doesn’t break the translation
  • the message is extracted as a whole sentence (this seems to be obvious, but most i18n libs simply split message into pieces by tags and translate them separately)

Plural

Plural
Props:
  • value (number) – (required) Value is mapped to plural form below
  • format (string|Object) – Number format passed as options to Intl.NumberFormat
  • offset (number) – Offset of value when calculating plural forms
  • zero (string) – Form for empty value
  • one (string) – Singular form
  • two (string) – Dual form
  • few (string) – Paucal form
  • many (string) – Plural form
  • other (string) – (required) general plural form
  • _<number> (string) – Exact match form, corresponds to =N rule

MessageFormat: {arg, plural, ...forms}

Props of <Plural> macro are transformed into plural format.

import { Plural } from "@lingui/macro"

<Plural value={numBooks} one="Book" other="Books" />
// ↓ ↓ ↓ ↓ ↓ ↓
// <Trans id="{numBooks, plural, one {Book} other {Books}}" values={{ numBooks }} />

# are formatted using number format. format prop is passed to this formatter.

Exact matches in MessageFormat syntax are expressed as =int (e.g. =0), but in React this isn’t a valid prop name. Therefore, exact matches are expressed as _int prop (e.g. _0). This is commonly used in combination with offset prop. offset affects only plural forms, not exact matches.

import { Plural } from "@lingui/macro"

const count = 42

<Plural
    value={count}
    offset={1}
    // when value == 0
    _0="Nobody arrived"

    // when value == 1
    _1="Only you arrived"

    // when value == 2
    // value - offset = 1 -> `one` plural form
    one="You and # other guest arrived"

    // when value >= 3
    other="You and # other guests arrived"
/>

// This is transformed to Trans component with ID:
// {count, plural, _0    {Nobody arrived}
//                 _1    {Only you arrived}
//                 one   {You and # other guest arrived}
//                 other {You and # other guests arrived}}

Select

Select
Props:
  • value (number) – (required) Value determines which form is outputted
  • other (number) – (required) Default, catch-all form

MessageFormat: {arg, select, ...forms}

Props of <Select> macro are transformed into select format:

import { Select } from "@lingui/macro"

// gender == "female"      -> Her book
// gender == "male"        -> His book
// gender == "unspecified" -> Their book
<Select
    value={gender}
    male="His book"
    female="Her book"
    other="Their book"
/>

SelectOrdinal

SelectOrdinal
Props:
  • value (number) – (required) Value is mapped to plural form below
  • offset (number) – Offset of value for plural forms
  • zero (string) – Form for empty value
  • one (string) – Singular form
  • two (string) – Dual form
  • few (string) – Paucal form
  • many (string) – Plural form
  • other (string) – (required) general plural form
  • _<number> (string) – Exact match form, correspond to =N rule. (e.g: _0, _1)
  • format (string|Object) – Number format passed as options to Intl.NumberFormat

MessageFormat: {arg, selectordinal, ...forms}

Props of <SelectOrdinal> macro are transformed into selectOrdinal format:

import { SelectOrdinal } from "@lingui/macro"

// count == 1 -> 1st
// count == 2 -> 2nd
// count == 3 -> 3rd
// count == 4 -> 4th
<SelectOrdinal
    value={count}
    one="1st"
    two="2nd"
    few="3rd"
    other="#th"
/>

DateFormat

DateFormat
Props:
  • value (string|Date) – (required) date to be formatted
  • format (string|Object) – date format passed as options to Intl.DateTimeFormat

<DateFormat> macro is transformed into date format.

// date as a string
<DateFormat value="2018-07-23" />;

const now = new Date();
// default language format
<DateFormat value={now} />;

const now = new Date();
// custom format
<DateFormat value={now} format={{
    year: "numeric",
    month: "long",
    day: "numeric"
}} />;

Note

Standalone <DateFormat> is transformed to <DateFormat> which is evaluated directly. It’s never transformed to {value, date} message, because such message can’t be translated.

NumberFormat

NumberFormat
Props:
  • value (number) – (required) Number to be formatted
  • format (string|Object) – Number format passed as options to Intl.NumberFormat

<NumberFormat> macro is transformed into number format.

const num = 0.42;
// default language format
<NumberFormat value={num} />;

const amount = 3.14;
// custom format
<NumberFormat value={amount} format={{
    style: 'currency',
    currency: 'EUR',
    minimumFractionDigits: 2
}} />;