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Decode strings according to the WHATWG Encoding Standard

Version published
Install size
395 kB

Package description

What is whatwg-encoding?

The whatwg-encoding npm package is a JavaScript implementation of the WHATWG Encoding Standard. It allows for encoding and decoding of text using various character encodings as specified by the standard.

What are whatwg-encoding's main functionalities?

Text Decoding

This feature allows you to decode a Uint8Array of text data into a string using a specified encoding. In the code sample, a Uint8Array representing the UTF-8 encoded string 'Hello' is decoded back into a JavaScript string.

"use strict";
const { decode } = require('whatwg-encoding');
const uint8Array = new Uint8Array([0x48, 0x65, 0x6c, 0x6c, 0x6f]);
const text = decode(uint8Array, 'utf-8');
console.log(text); // 'Hello'

Text Encoding

This feature allows you to encode a JavaScript string into a Uint8Array using a specified encoding. In the code sample, the string 'Hello' is encoded into a Uint8Array using UTF-8 encoding.

"use strict";
const { encode } = require('whatwg-encoding');
const text = 'Hello';
const uint8Array = encode(text, 'utf-8');
console.log(uint8Array); // Uint8Array showing the bytes of the encoded string

Other packages similar to whatwg-encoding



Decode According to the WHATWG Encoding Standard

This package provides a thin layer on top of iconv-lite which makes it expose some of the same primitives as the Encoding Standard.

const whatwgEncoding = require("whatwg-encoding");

console.assert(whatwgEncoding.labelToName("latin1") === "windows-1252");
console.assert(whatwgEncoding.labelToName("  CYRILLic ") === "ISO-8859-5");

console.assert(whatwgEncoding.isSupported("IBM866") === true);

// Not supported by the Encoding Standard
console.assert(whatwgEncoding.isSupported("UTF-32") === false);

// In the Encoding Standard, but this package can't decode it
console.assert(whatwgEncoding.isSupported("x-mac-cyrillic") === false);

console.assert(whatwgEncoding.getBOMEncoding(new Uint8Array([0xFE, 0xFF])) === "UTF-16BE");
console.assert(whatwgEncoding.getBOMEncoding(new Uint8Array([0x48, 0x69])) === null);

console.assert(whatwgEncoding.decode(new Uint8Array([0x48, 0x69]), "UTF-8") === "Hi");


  • decode(uint8Array, fallbackEncodingName): performs the decode algorithm (in which any BOM will override the passed fallback encoding), and returns the resulting string
  • labelToName(label): performs the get an encoding algorithm and returns the resulting encoding's name, or null for failure
  • isSupported(name): returns whether the encoding is one of the encodings of the Encoding Standard, and is an encoding that this package can decode (via iconv-lite)
  • getBOMEncoding(uint8Array): sniffs the first 2–3 bytes of the supplied Uint8Array, returning one of the encoding names "UTF-8", "UTF-16LE", or "UTF-16BE" if the appropriate BOM is present, or null if no BOM is present

Unsupported encodings

Since we rely on iconv-lite, we are limited to support only the encodings that they support. Currently we are missing support for:

  • ISO-2022-JP
  • ISO-8859-8-I
  • replacement
  • x-mac-cyrillic
  • x-user-defined

Passing these encoding names will return false when calling isSupported, and passing any of the possible labels for these encodings to labelToName will return null.


This package was originally based on the excellent work of @nicolashenry, in jsdom. It has since been pulled out into this separate package.


If you are looking for a JavaScript implementation of the Encoding Standard's TextEncoder and TextDecoder APIs, you'll want @inexorabletash's text-encoding package. Node.js also has them built-in.



Last updated on 12 Nov 2023

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