mutf-8: An Encoder and Decoder for Modified UTF-8

What is Modified UTF-8?

Modified UTF-8 is a variant of UTF-8 used in the Java platform, such as the class file format and object serialization.

See The Java Virtual Machine Specification, Java SE 21 Edition, Section 4.4.7 for details.

Installation

npm install mutf-8

If you want to use the stream API, install the mutf-8-stream module instead.

npm install mutf-8-stream

Usage

The APIs are similar to WHATWG Encoding.

import { MUtf8Decoder, MUtf8Encoder } from "mutf-8";

const encoder = new MUtf8Encoder();
const code = encoder.encode("Hello 世界! Santé🍻");
// Uint8Array:
//   0x48 0x65 0x6c 0x6c 0x6f 0x20 0xe4 0xb8
//   0x96 0xe7 0x95 0x8c 0x21 0x20 0x53 0x61
//   0x6e 0x74 0xc3 0xa9 0xed 0xa0 0xbc 0xed
//   0xbd 0xbb

const decoder = new MUtf8Decoder();
const text = decoder.decode(code);
// string:
//   Hello 世界! Santé🍻

import { MUtf8DecoderStream, MUtf8EncoderStream } from "mutf-8-stream";

await getLargeTextAsStream()
  .pipeThrough(new MUtf8EncoderStream())
  .pipeTo(new WritableStream({
    write(chunk) {
      // Handle the encoded chunk
    }
  }));

await getLargeBinaryAsStream()
  .pipeThrough(new MUtf8DecoderStream())
  .pipeTo(new WritableStream({
    write(chunk) {
      // Handle the decoded chunk
    }
  }));

See API Reference for details.

License

This library is licensed under the MIT License.

Copyright (c) 2025 sciencesakura