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Macros

@lingui/macro package provides babel macros which transforms JavaScript objects and JSX elements into messages in ICU MessageFormat.

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 dev dependency and @lingui/macro as dependency:

    npm install --save-dev babel-plugin-macros
    npm install --save @lingui/macro
    note

    It's recommended to install @lingui/macro package as a production dependency rather than development one to avoid import/no-extraneous-dependencies errors in ESLint.

  2. Add macros to the top of plugins section in your Babel config:

    {
       "plugins": [
          "macros"
       ]
    }

Overview​

The advantages of using macros are:

  • You don't need to learn ICU MessageFormat syntax. You always use familiar JS and JSX code.
  • Components and functions are type checked.
  • Additional validation of plural rules is performed during transformation.
  • Non essentials data are removed from production build (e.g. comments and default messages) to shave few bytes.

JSX macros are transformed to Trans component from @lingui/react:

import { Trans } from "@lingui/macro"
<Trans>Attachment {name} saved</Trans>

// ↓ ↓ ↓ ↓ ↓ ↓

import { Trans } from "@lingui/react"
<Trans id="Attachment {name} saved" values={{ name }} />

JS macros (i.e. macros that looks like a simple JavaScript functions) are transformed into i18n._ call.

import { t } from "@lingui/macro"
t`Attachment ${name} saved`

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
/*i18n*/
i18n._("Attachment {name} saved", { name })
note

By default, the i18n object is imported from @lingui/core. If you use a custom instance of i18n object, you need to set runtimeConfigModule or pass a custom instance to t.

The only exception is defineMessage which is transformed into message descriptor. In other words, the message isn't translated directly and can be used anytime later:

import { i18n } from "@lingui/core"
import { defineMessage } from "@lingui/macro"

// define message
const message = defineMessage({ message: `Attachment ${name} saved` })

// translate it
i18n._(message)

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"

// define message
const message = /*i18n*/{ id: "Attachment {name} saved", values: { name }})

// translate it
i18n._(message)

Examples of JS macros​

t`Refresh inbox`

// ↓ ↓ ↓ ↓ ↓ ↓

/*i18n*/
i18n._("Refresh inbox")
t`Attachment ${name} saved`

// ↓ ↓ ↓ ↓ ↓ ↓

/*i18n*/
i18n._("Attachment {name} saved", { name })
t(customI18n)`Refresh inbox`

// ↓ ↓ ↓ ↓ ↓ ↓

/*i18n*/
customI18n._("Refresh inbox")
t(customI18n)`Attachment ${name} saved`

// ↓ ↓ ↓ ↓ ↓ ↓

/*i18n*/
customI18n._("Attachment {name} saved", { name })
plural(count, {
  one: "Message",
  other: "Messages"
})

// ↓ ↓ ↓ ↓ ↓ ↓

/*i18n*/
i18n._("{count, plural, one {Message} other {Messages}}", {
  count
})
t({
  id: "msg.refresh",
  message: "Refresh inbox"
})

// ↓ ↓ ↓ ↓ ↓ ↓

i18n._(/*i18n*/{
  id: "msg.refresh",
  message: "Refresh inbox"
})
t(customI18n)({
  id: "msg.refresh",
  message: "Refresh inbox"
})

// ↓ ↓ ↓ ↓ ↓ ↓

customI18n._(/*i18n*/{
  id: "msg.refresh",
  message: "Refresh inbox"
})
defineMessage({
  id: "msg.refresh",
  message: "Refresh inbox"
})

// ↓ ↓ ↓ ↓ ↓ ↓

/*i18n*/{
  id: "msg.refresh",
  message: "Refresh inbox"
}

Examples of JSX macros​

<Trans>Attachment {name} saved</Trans>

// ↓ ↓ ↓ ↓ ↓ ↓

<Trans
   id="Attachment {name} saved"
   values={{ name }}
/>
<Plural
   value={count}
   one="Message"
   other="Messages"
/>

// ↓ ↓ ↓ ↓ ↓ ↓

<Trans
   id="{count, plural, one { Message} other {Messages}}"
   values={{ count }}
/>
<Trans id="msg.refresh">
   Refresh inbox
</Trans>

// ↓ ↓ ↓ ↓ ↓ ↓

<Trans
   id="msg.refresh"
   message="Refresh inbox"
/>

JS macros​

These macros can be used in any context (e.g. outside JSX). All JS macros are transformed into a Message Descriptor wrapped inside of i18n._ call.

note

By default, the i18n object is imported from @lingui/core. If you use a custom instance of i18n object, you need to set runtimeConfigModule or pass a custom instance to t.

Message Descriptor is an object with message ID, default message and other parameters. i18n._ accepts message descriptors and performs translation and formatting:

type MessageDescriptor = {
   id: String,
   message?: String,
   values?: Object,
   formats?: Object,
   comment?: string
}

id is message ID and the only required parameter. id and message 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.

Note

i18n comment

In the examples below you might notice /*i18n*/ comment in macro output. This comment tells the extract plugin that following object or string should be collected to message catalog.

t​

The most common macro for messages. It transforms tagged template literal into message in ICU MessageFormat:

import { t } from "@lingui/macro"
const message = t`Hello World`

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._("Hello World")

Message variables are supported:

import { t } from "@lingui/macro"
const message = t`My name is ${name}`

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._("My name is {name}", {
  name
})

In fact, any expression can be used inside template literal. However, only simple variables are referenced by name in a transformed message. All other expressions are referenced by numeric index:

import { t } from "@lingui/macro"
const message = t`Today is ${new Date()}`

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core";

const message =
/*i18n*/
i18n._("Today is {0}", {
  0: new Date()
});

Optionally, a custom i18n instance can be passed that can be used instead of the global instance:

import { t } from "@lingui/macro"
import { i18n } from "./lingui"
const message = t(i18n)`Hello World`

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "./lingui"
const message =
/*i18n*/
i18n._("Hello World")

It's also possible to pass custom id and comment for translators by calling t macro with a message descriptor:

import { t } from "@lingui/macro"
const message = t({
   id: 'msg.hello',
   comment: 'Greetings at the homepage',
   message: `Hello ${name}`
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message = i18n._(/*i18n*/{
   id: 'msg.hello',
   comment: 'Greetings at the homepage',
   message: 'Hello {name}',
   values: { name }
})

In this case the message is used as a default message and it's transformed as if it were wrapped in t macro. message also accepts any other macros:

import { t } from "@lingui/macro"
const message = t({
   id: 'msg.plural',
   message: plural(value, { one: "...", other: "..." })
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message = i18n._(/*i18n*/{
   id: 'msg.plural',
   message: '{value, plural, one {...} other {...}}',
   values: { value }
})

plural​

plural(value: string | number, options: Object)

plural macro is used for pluralization, e.g: messages which has different form based on counter. The first argument value determines the plural form. The second argument is an object with available plural forms. Plural form used in the source code depends on your source locale (e.g. English has only one and other).

import { plural } from "@lingui/macro"
const message = plural(count, {
   one: "# Book",
   other: "# Books"
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._('{count, plural, one {# Book} other {# Books}}', {
  count
})

If you need to add variables to plural form, you can use template string literals. This time t macro isn't required as template strings are transformed automatically:

import { plural } from "@lingui/macro"
const message = plural(count, {
   one: `${name} has # friend`,
   other: `${name} has # friends`
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._('{count, plural, one {{name} has # friend} other {{name} has # friends}}', {
  count, name
})

Plurals can also be nested to form complex messages. Here's an example using two counters:

import { plural } from "@lingui/macro"
const message = plural(numBooks, {
   one: plural(numArticles, {
      one: `1 book and 1 article`,
      other: `1 book and ${numArticles} articles`,
   }),
   other: plural(numArticles, {
      one: `${numBooks} books and 1 article`,
      other: `${numBooks} books and ${numArticles} articles`,
   }),
})

// ↓ ↓ ↓ ↓ ↓ ↓
// Generated message was wrapped for better readability

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._(`{numBooks, plural,
         one {{numArticles, plural,
            one {1 book and 1 article}
            other {1 book and {numArticles} articles}
         }}
         other {{numArticles, plural,
            one {{numBooks} books and 1 article}
            other {{numBooks} books and {numArticles} articles}
         }}
      }`,
  { numBooks, numArticles }
)
tip

This is just an example how macros can be combined to create a complex messages. However, simple is better because in the end it's the translator who's gonna have to translate these long and complex strings.

caution

Use plural inside t macro if you want to add custom id or comment for translators.

selectOrdinal​

selectOrdinal(value: string | number, options: Object)

selectOrdinal macro is similar to plural but instead of using cardinal plural forms it uses ordinal forms:

import { selectOrdinal } from "@lingui/macro"
const message = selectOrdinal(count, {
   one: "#st",
   two: "#nd",
   few: "#rd",
   other: "#th",
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._('{count, selectOrdinal, one {#st} two {#nd} few {#rd} other {#th}}', {
  count
})
caution

Use selectOrdinal inside t macro if you want to add custom id or comment for translators.

select​

select(value: string | number, options: Object)

select macro works as a switch statement — it select one of the forms provided in options object which key matches exactly value:

import { select } from "@lingui/macro"
const message = select(gender, {
   male: "he",
   female: "she",
   other: "they"
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message =
/*i18n*/
i18n._('{gender, select, male {he} female {she} other {they}}', {
  gender
})
caution

Use select inside t macro if you want to add custom id or comment for translators.

defineMessage​

defineMessage macro is a wrapper around macros above which allows you to add comments for translators or override the message ID.

Unlike the other JS macros, it doesn't wrap generated MessageDescription into i18n._ call.

type MessageDescriptor = {
  id?: string,
  message?: string,
  comment?: string
}

defineMessage(message: MessageDescriptor)

Either id or message property is required. id is a custom message id. If it isn't set, the message is used instead.

import { defineMessage } from "@lingui/macro"
const message = defineMessage({
   id: "Navigation / About",
   message: "About us"
})

// ↓ ↓ ↓ ↓ ↓ ↓

const message = /*i18n*/{
  id: 'Navigation / About',
  message: "About us"
}

message is the default message. Any JS macro can be used here. Template string literals don't need to be tagged with t.

import { defineMessage, t } from "@lingui/macro"

const name = "Joe"

const message = defineMessage({
   comment: "Greetings on the welcome page",
   message: `Welcome, ${name}!`
})

// ↓ ↓ ↓ ↓ ↓ ↓

const message = /*i18n*/{
   comment: "Greetings on the welcome page",
   message: "Welcome, {name}",
   values: {
     name
   }
}

comment is a comment for translators. It's extracted to the message catalog and it gives extra context for translators. It's removed from production code:

import { defineMessage } from "@lingui/macro"
const message = defineMessage({
   comment: "Link in navigation pointing to About page",
   message: "About us"
})

// ↓ ↓ ↓ ↓ ↓ ↓

const message = /*i18n*/{
  comment: "Link in navigation pointing to About page",
  id: "About us"
}
Note

In production build, the whole macro is replaced with an id:

import { defineMessage } from "@lingui/macro"
const message = defineMessage({
   id: "Navigation / About",
   comment: "Link in navigation pointing to About page",
   message: "About us"
})

// process.env.NODE_ENV === "production"
// ↓ ↓ ↓ ↓ ↓ ↓

const message = "Navigation / About"

message and comment are used in message catalogs only.

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>

// ↓ ↓ ↓ ↓ ↓ ↓
import { Trans } from "@lingui/react"
<Trans id="message.attachment_saved" message="Attachment {name} saved." />

comment​

Comment for translators to give them additional context about the message. It's removed from production code.

render​

Render prop function used to render translation. This prop is directly passed to Trans component from @lingui/react. See rendering of translations for more info.

Trans​

Prop nameTypeDescription
idstringCustom message ID
commentstringComment for translators

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>;

// ↓ ↓ ↓ ↓ ↓ ↓
import { Trans } from "@lingui/react"
<Trans id="Refresh inbox" />

Custom id is preserved:

import { Trans } from "@lingui/macro"
<Trans id="message.attachment_saved">Attachment {name} saved.</Trans>

// ↓ ↓ ↓ ↓ ↓ ↓

import { Trans } from "@lingui/react"
<Trans id="message.attachment_saved" message="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>;

// ↓ ↓ ↓ ↓ ↓ ↓

import { Trans } from "@lingui/macro"
<Trans id="Read the <0>docs</0>." components={{0: <a href="/docs" />}} />

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

  • 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​

Prop nameTypeDescription
valuenumber(required) Value is mapped to plural form below
formatstring|ObjectNumber format passed as options to Intl.NumberFormat
offsetnumberOffset of value when calculating plural forms
zerostringForm for empty value
onestringSingular form
twostringDual form
fewstringPaucal form
manystringPlural form
otherstring(required) general plural form
_<number>stringExact 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" />

// ↓ ↓ ↓ ↓ ↓ ↓
import { Trans } from "@lingui/react"
<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"

<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, offset:1 _0    {Nobody arrived}
                           _1    {Only you arrived}
                           one   {You and # other guest arrived}
                           other {You and # other guests arrived}}
*/

SelectOrdinal​

Prop nameTypeDescription
valuenumber(required) Value is mapped to plural form below
offsetnumberOffset of value for plural forms
zerostringForm for empty value
onestringSingular form
twostringDual form
fewstringPaucal form
manystringPlural form
otherstring(required) general plural form
_<number>stringExact match form, correspond to =N rule. (e.g: _0, _1)
formatstring|ObjectNumber 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="#st"
    two="#nd"
    few="#rd"
    other="#th"
/>

Select​

Prop nameTypeDescription
valuenumber(required) Value determines which form is outputted
othernumber(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"
/>