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utf8.js Build status Code coverage status Dependency status

utf8.js is a well-tested UTF-8 encoder/decoder written in JavaScript. Unlike many other JavaScript solutions, it is designed to be a proper UTF-8 encoder/decoder: it can encode/decode any scalar Unicode code point values, as per the Encoding Standard. Here’s an online demo.

Feel free to fork if you see possible improvements!


Via npm:

npm install utf8

In a browser:

<script src="utf8.js"></script>

In Node.js:

const utf8 = require('utf8');



Encodes any given JavaScript string (string) as UTF-8, and returns the UTF-8-encoded version of the string. It throws an error if the input string contains a non-scalar value, i.e. a lone surrogate. (If you need to be able to encode non-scalar values as well, use WTF-8 instead.)

// → '\xC2\xA9'
// U+10001 LINEAR B SYLLABLE B038 E; see
// → '\xF0\x90\x80\x81'


Decodes any given UTF-8-encoded string (byteString) as UTF-8, and returns the UTF-8-decoded version of the string. It throws an error when malformed UTF-8 is detected. (If you need to be able to decode encoded non-scalar values as well, use WTF-8 instead.)

// → '\xA9'

// → '\uD800\uDC01'
// → U+10001 LINEAR B SYLLABLE B038 E


A string representing the semantic version number.


utf8.js has been tested in at least Chrome 27-39, Firefox 3-34, Safari 4-8, Opera 10-28, IE 6-11, Node.js v0.10.0, Narwhal 0.3.2, RingoJS 0.8-0.11, PhantomJS 1.9.0, and Rhino 1.7RC4.

Unit tests & code coverage

After cloning this repository, run npm install to install the dependencies needed for development and testing. You may want to install Istanbul globally using npm install istanbul -g.

Once that’s done, you can run the unit tests in Node using npm test or node tests/tests.js. To run the tests in Rhino, Ringo, Narwhal, PhantomJS, and web browsers as well, use grunt test.

To generate the code coverage report, use grunt cover.


Why is the first release named v2.0.0? Haven’t you heard of semantic versioning?

Long before utf8.js was created, the utf8 module on npm was registered and used by another (slightly buggy) library. @ryanmcgrath was kind enough to give me access to the utf8 package on npm when I told him about utf8.js. Since there has already been a v1.0.0 release of the old library, and to avoid breaking backwards compatibility with projects that rely on the utf8 npm package, I decided the tag the first release of utf8.js as v2.0.0 and take it from there.


Mathias Bynens


utf8.js is available under the MIT license.