目录

• Internationalization Support

  • Options for building Node.js

    • Disable all internationalization features (none)
    • Build with a pre-installed ICU (system-icu)

    • Embed a limited set of ICU data (small-icu)

      • Providing ICU data at runtime
    • Embed the entire ICU (full-icu)
  • Detecting internationalization support

Internationalization Support#

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Node.js有许多功能，使它更容易编写国际化程序.其中一些是：

• ECMAScript语言规格中的本地化敏感或感知统一编码功能：

  • String.prototype.normalize()
  • String.prototype.toLowerCase()
  • String.prototype.toUpperCase()

• ECMAScript国际化API规格 (aka ECMA-402)中的所有的功能：

  • Intl 对象 -本地化敏感的方法如String.prototype.localeCompare() 和 Date.prototype.toLocaleString()
• WHATWG URL解析器的国际化域名 （IDN）的支持
• require('buffer').transcode()
• 更准确的REPL 行编辑
• require('util').TextDecoder

Node.js（及其背后的V8引擎）在原生的C / C++代码使用ICU 实施这些功能。 然而，其中一些为了支持世界的所有地区，需要一个非常大的ICU数据文件。 因为预计多数Node.js的用户将只使用ICU的功能的一小部分，Node.js默认设置了所有ICU的数据集的一个子集。 当建设或运行Node.js时提供了几个定制和扩展ICU数据集的选项。

Options for building Node.js#

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To control how ICU is used in Node.js, four configure options are available during compilation. Additional details on how to compile Node.js are documented in BUILDING.md.

• --with-intl=none/--without-intl
• --with-intl=system-icu
• --with-intl=small-icu (default)
• --with-intl=full-icu

An overview of available Node.js and JavaScript features for each configure option:

	none	system-icu	small-icu	full-icu
String.prototype.normalize()	none (function is no-op)	full	full	full
String.prototype.to*Case()	full	full	full	full
Intl	none (object does not exist)	partial/full (depends on OS)	partial (English-only)	full
String.prototype.localeCompare()	partial (not locale-aware)	full	full	full
String.prototype.toLocale*Case()	partial (not locale-aware)	full	full	full
Number.prototype.toLocaleString()	partial (not locale-aware)	partial/full (depends on OS)	partial (English-only)	full
Date.prototype.toLocale*String()	partial (not locale-aware)	partial/full (depends on OS)	partial (English-only)	full
WHATWG URL Parser	partial (no IDN support)	full	full	full
require('buffer').transcode()	none (function does not exist)	full	full	full
REPL	partial (inaccurate line editing)	full	full	full
require('util').TextDecoder	partial (basic encodings support)	partial/full (depends on OS)	partial (Unicode-only)	full
RegExp Unicode Property Escapes	none (invalid RegExp error)	full	full	full

The "(not locale-aware)" designation denotes that the function carries out its operation just like the non-Locale version of the function, if one exists. For example, under none mode, Date.prototype.toLocaleString()'s operation is identical to that of Date.prototype.toString().

Disable all internationalization features (`none`)#

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If this option is chosen, most internationalization features mentioned above will be unavailable in the resulting node binary.

Build with a pre-installed ICU (`system-icu`)#

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Node.js can link against an ICU build already installed on the system. In fact, most Linux distributions already come with ICU installed, and this option would make it possible to reuse the same set of data used by other components in the OS.

Functionalities that only require the ICU library itself, such as String.prototype.normalize() and the WHATWG URL parser, are fully supported under system-icu. Features that require ICU locale data in addition, such as Intl.DateTimeFormat may be fully or partially supported, depending on the completeness of the ICU data installed on the system.

Embed a limited set of ICU data (`small-icu`)#

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This option makes the resulting binary link against the ICU library statically, and includes a subset of ICU data (typically only the English locale) within the node executable.

Functionalities that only require the ICU library itself, such as String.prototype.normalize() and the WHATWG URL parser, are fully supported under small-icu. Features that require ICU locale data in addition, such as Intl.DateTimeFormat, generally only work with the English locale:

const january = new Date(9e8);
const english = new Intl.DateTimeFormat('en', { month: 'long' });
const spanish = new Intl.DateTimeFormat('es', { month: 'long' });

console.log(english.format(january));
// Prints "January"
console.log(spanish.format(january));
// Prints "M01" on small-icu
// Should print "enero"

This mode provides a good balance between features and binary size, and it is the default behavior if no --with-intl flag is passed. The official binaries are also built in this mode.

Providing ICU data at runtime#

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If the small-icu option is used, one can still provide additional locale data at runtime so that the JS methods would work for all ICU locales. Assuming the data file is stored at /some/directory, it can be made available to ICU through either:

• The NODE_ICU_DATA environment variable:

  env NODE_ICU_DATA=/some/directory node
  

• The --icu-data-dir CLI parameter:

  node --icu-data-dir=/some/directory
  

(If both are specified, the --icu-data-dir CLI parameter takes precedence.)

ICU is able to automatically find and load a variety of data formats, but the data must be appropriate for the ICU version, and the file correctly named. The most common name for the data file is icudt5X[bl].dat, where 5X denotes the intended ICU version, and b or l indicates the system's endianness. Check "ICU Data" article in the ICU User Guide for other supported formats and more details on ICU data in general.

The full-icu npm module can greatly simplify ICU data installation by detecting the ICU version of the running node executable and downloading the appropriate data file. After installing the module through npm i full-icu, the data file will be available at ./node_modules/full-icu. This path can be then passed either to NODE_ICU_DATA or --icu-data-dir as shown above to enable full Intl support.

Embed the entire ICU (`full-icu`)#

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This option makes the resulting binary link against ICU statically and include a full set of ICU data. A binary created this way has no further external dependencies and supports all locales, but might be rather large. See BUILDING.md on how to compile a binary using this mode.

Detecting internationalization support#

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To verify that ICU is enabled at all (system-icu, small-icu, or full-icu), simply checking the existence of Intl should suffice:

const hasICU = typeof Intl === 'object';

Alternatively, checking for process.versions.icu, a property defined only when ICU is enabled, works too:

const hasICU = typeof process.versions.icu === 'string';

To check for support for a non-English locale (i.e. full-icu or system-icu), Intl.DateTimeFormat can be a good distinguishing factor:

const hasFullICU = (() => {
  try {
    const january = new Date(9e8);
    const spanish = new Intl.DateTimeFormat('es', { month: 'long' });
    return spanish.format(january) === 'enero';
  } catch (err) {
    return false;
  }
})();

For more verbose tests for Intl support, the following resources may be found to be helpful:

• btest402: Generally used to check whether Node.js with Intl support is built correctly.
• Test262: ECMAScript's official conformance test suite includes a section dedicated to ECMA-402.