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author | Timothy Gu <timothygu99@gmail.com> | 2017-06-26 08:05:49 +0300 |
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committer | Timothy Gu <timothygu99@gmail.com> | 2017-07-06 06:19:34 +0300 |
commit | 6809429cfa035b35ca8c83815e644234092f53be (patch) | |
tree | 16433b0dd64a70eaa937f738c1b5116f424cd26b /doc/api/intl.md | |
parent | 34cf8ad73d005d86458124ab5c6b62a0aab7ed8e (diff) |
doc: add documentation on ICU
PR-URL: https://github.com/nodejs/node/pull/13916
Refs: https://github.com/nodejs/node/pull/13644#discussion_r121616327
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Diffstat (limited to 'doc/api/intl.md')
-rw-r--r-- | doc/api/intl.md | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/doc/api/intl.md b/doc/api/intl.md new file mode 100644 index 00000000000..c0d6b822892 --- /dev/null +++ b/doc/api/intl.md @@ -0,0 +1,209 @@ +# Internationalization Support + +Node.js has many features that make it easier to write internationalized +programs. Some of them are: + +- Locale-sensitive or Unicode-aware functions in the [ECMAScript Language + Specification][ECMA-262]: + - [`String.prototype.normalize()`][] + - [`String.prototype.toLowerCase()`][] + - [`String.prototype.toUpperCase()`][] +- All functionality described in the [ECMAScript Internationalization API + Specification][ECMA-402] (aka ECMA-402): + - [`Intl`][] object + - Locale-sensitive methods like [`String.prototype.localeCompare()`][] and + [`Date.prototype.toLocaleString()`][] +- The [WHATWG URL parser][]'s [internationalized domain names][] (IDNs) support +- [`require('buffer').transcode()`][] +- More accurate [REPL][] line editing + +Node.js (and its underlying V8 engine) uses [ICU][] to implement these features +in native C/C++ code. However, some of them require a very large ICU data file +in order to support all locales of the world. Because it is expected that most +Node.js users will make use of only a small portion of ICU functionality, only +a subset of the full ICU data set is provided by Node.js by default. Several +options are provided for customizing and expanding the ICU data set either when +building or running Node.js. + +## Options for building Node.js + +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 + +*Note*: 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`) + +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`) + +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`) + +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: + +```js +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 + +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`][] environmental variable: + + ```shell + env NODE_ICU_DATA=/some/directory node + ``` + +* The [`--icu-data-dir`][] CLI parameter: + + ```shell + 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`) + +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][BUILDING.md#full-icu] on how to compile a binary using this mode. + +## Detecting internationalization support + +To verify that ICU is enabled at all (`system-icu`, `small-icu`, or +`full-icu`), simply checking the existence of `Intl` should suffice: + +```js +const hasICU = typeof Intl === 'object'; +``` + +Alternatively, checking for `process.versions.icu`, a property defined only +when ICU is enabled, works too: + +```js +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: + +```js +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. + +[btest402]: https://github.com/srl295/btest402 +[BUILDING.md]: https://github.com/nodejs/node/blob/master/BUILDING.md +[BUILDING.md#full-icu]: https://github.com/nodejs/node/blob/master/BUILDING.md#build-with-full-icu-support-all-locales-supported-by-icu +[`Date.prototype.toLocaleString()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleString +[ECMA-262]: https://tc39.github.io/ecma262/ +[ECMA-402]: https://tc39.github.io/ecma402/ +[full-icu]: https://www.npmjs.com/package/full-icu +[ICU]: http://icu-project.org/ +["ICU Data"]: http://userguide.icu-project.org/icudata +[`--icu-data-dir`]: cli.html#cli_icu_data_dir_file +[internationalized domain names]: https://en.wikipedia.org/wiki/Internationalized_domain_name +[`Intl`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Intl +[`Intl.DateTimeFormat`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DateTimeFormat +[`NODE_ICU_DATA`]: cli.html#cli_node_icu_data_file +[`Number.prototype.toLocaleString()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Number/toLocaleString +[REPL]: repl.html#repl_repl +[`require('buffer').transcode()`]: buffer.html#buffer_buffer_transcode_source_fromenc_toenc +[`String.prototype.localeCompare()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare +[`String.prototype.normalize()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/normalize +[`String.prototype.toLowerCase()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase +[`String.prototype.toUpperCase()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase +[Test262]: https://github.com/tc39/test262/tree/master/test/intl402 +[WHATWG URL parser]: url.html#url_the_whatwg_url_api |