ICU StringPrep profiles for NodeJS
JavaScript C++ Python



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Exposes predefined Unicode normalization functions that are required by many protocols. This is just a binding to ICU, which is said to be fast..

If ICU is not available then we make use of JavaScript fallbacks.


    var StringPrep = require('node-stringprep').StringPrep;
    var prep = new StringPrep('nameprep');
    prep.prepare('Äffchen')  // => 'äffchen'

For a list of supported profiles, see

Javascript fallbacks can be disabled/enabled using the following methods on the StringPrep object:

var prep = new StringPrep('resourceprep')

Javascript fallbacks are enabled by default. You can also check to see if native icu bindings can/will be used by calling the isNative() method:

var prep = new StringPrep('resourceprep')
prep.isNative()  // true or false

We also implement the ToASCII and ToUnicode operations as defined in the IDNA RFC 3490. These routines convert Unicode to ASCII with NamePrep and then with Punycode, and vice versa.

    var nodeStringPrep = require('node-stringprep');
    nodeStringPrep.toASCII('i♥u') // 'xn--iu-t0x'
    nodeStringPrep.toUnicode('xn--iu-t0x') // 'i♥u'

The operations can be finessed with an optional second argument, a set of boolean flags:

    nodeStringPrep.toASCII('i♥u', {
        allowUnassigned: true, // allow unassigned code points to be converted
        throwIfError: true, // throw exception if error, don't return string unchanged
        useSTD3Rules: true // use the STD3 ASCII rules for host names
    nodeStringPrep.toUnicode('xn--iu-t0x', {
        allowUnassigned: true // allow unassigned code points to be converted


    npm i node-stringprep

If libicu isn't available installation will gracefully fail and javascript fallbacks will be used.

If experiencing issues with node-gyp please see which may be able to help.


    apt-get install libicu-dev

RedHat & Centos

    yum install libicu-devel


    emerge icu



    port install icu +devel


    sudo ln -s /opt/boxen/homebrew/Cellar/icu4c/52.1/bin/icu-config /usr/local/bin/icu-config
    sudo ln -s /opt/boxen/homebrew/Cellar/icu4c/52.1/include/* /usr/local/include


brew install icu4c
ln -s /usr/local/Cellar/icu4c/<VERSION>/bin/icu-config /usr/local/bin/icu-config
ln -s /usr/local/Cellar/icu4c/<VERSION>/include/* /usr/local/include

If experiencing issues with 'homebrew' installing version 50.1 of icu4c, try the following:

    brew search icu4c
    brew tap homebrew/versions
    brew versions icu4c
    cd $(brew --prefix) && git pull --rebase
    git checkout c25fd2f $(brew --prefix)/Library/Formula/icu4c.rb
    brew install icu4c

Running Tests

npm test