@msgpack/msgpack - MessagePack for JavaScript/TypeScript/ECMA-262 / msgpack.org[JavaScript]

MessagePack for JavaScript/ECMA-262

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This is a JavaScript/ECMA-262 implementation of MessagePack, an efficient binary serilization format:


This library is a universal JavaScript, meaning it is compatible with all the major browsers and NodeJS. In addition, because it is implemented in TypeScript, type definition files (d.ts) are bundled in the distribution.

Note that this is the second version of MessagePack for JavaScript. The first version, which was implemented in ES5 and was never released to npmjs.com, is tagged as classic.


import { deepStrictEqual } from "assert";
import { encode, decode } from "@msgpack/msgpack";

const object = {
  nil: null,
  integer: 1,
  float: Math.PI,
  string: "Hello, world!",
  binary: Uint8Array.from([1, 2, 3]),
  array: [10, 20, 30],
  map: { foo: "bar" },
  timestampExt: new Date(),

const encoded: Uint8Array = encode(object);

deepStrictEqual(decode(encoded), object);

Table of Contents


This library is published to npmjs.com as @msgpack/msgpack.

npm install @msgpack/msgpack


encode(data: unknown, options?: EncodeOptions): Uint8Array

It encodes data into a single MessagePack-encoded object, and returns a byte array as Uint8Array, throwing errors if data is, or includes, a non-serializable object such as a function or a symbol.

for example:

import { encode } from "@msgpack/msgpack";

const encoded: Uint8Array = encode({ foo: "bar" });

If you'd like to convert an uint8array to a NodeJS Buffer, use Buffer.from(arrayBuffer, offset, length) in order not to copy the underlying ArrayBuffer, while Buffer.from(uint8array) copies it:

import { encode } from "@msgpack/msgpack";

const encoded: Uint8Array = encode({ foo: "bar" });

// `buffer` refers the same ArrayBuffer as `encoded`.
const buffer: Buffer = Buffer.from(encoded.buffer, encoded.byteOffset, encoded.byteLength);


Name Type Default
extensionCodec ExtensionCodec ExtensionCodec.defaultCodec
maxDepth number 100
initialBufferSize number 2048
sortKeys boolean false
forceFloat32 boolean false
forceIntegerToFloat boolean false
ignoreUndefined boolean false
context user-defined -

decode(buffer: ArrayLike<number> | BufferSource, options?: DecodeOptions): unknown

It decodes buffer that includes a MessagePack-encoded object, and returns the decoded object typed unknown.

buffer must be an array of bytes, which is typically Uint8Array or ArrayBuffer. BufferSource is defined as ArrayBuffer | ArrayBufferView.

In addition, buffer can include a single encoded object. If the buffer includes extra bytes after an object, it will throw RangeError. To decode buffer that includes multiple encoded objects, use decodeMulti() or decodeMultiStream() (recommended) instead.

for example:

import { decode } from "@msgpack/msgpack";

const encoded: Uint8Array;
const object = decode(encoded);

NodeJS Buffer is also acceptable because it is a subclass of Uint8Array.


Name Type Default
extensionCodec ExtensionCodec ExtensionCodec.defaultCodec
maxStrLength number 4_294_967_295 (UINT32_MAX)
maxBinLength number 4_294_967_295 (UINT32_MAX)
maxArrayLength number 4_294_967_295 (UINT32_MAX)
maxMapLength number 4_294_967_295 (UINT32_MAX)
maxExtLength number 4_294_967_295 (UINT32_MAX)
context user-defined -

You can use max${Type}Length to limit the length of each type decoded.

decodeMulti(buffer: ArrayLike<number> | BufferSource, options?: DecodeOptions): Generator<unknown, void, unknown>

It decodes buffer that includes multiple MessagePack-encoded objects, and returns decoded objects as a generator. That is, this is a synchronous variant for decodeMultiStream().

This function is not recommended to decode a MessagePack binary via I/O stream including sockets because it's synchronous. Instead, decodeMultiStream() decodes it asynchronously, typically spending less time and memory.

for example:

import { decode } from "@msgpack/msgpack";

const encoded: Uint8Array;

for (const object of decodeMulti(encoded)) {

decodeAsync(stream: ReadableStreamLike<ArrayLike<number> | BufferSource>, options?: DecodeAsyncOptions): Promise<unknown>

It decodes stream, where ReadableStreamLike<T> is defined as ReadableStream<T> | AsyncIterable<T>, in an async iterable of byte arrays, and returns decoded object as unknown type, wrapped in Promise. This function works asynchronously. This is an async variant for decode().

DecodeAsyncOptions is the same as DecodeOptions for decode().

This function is designed to work with whatwg fetch() like this:

import { decodeAsync } from "@msgpack/msgpack";

const MSGPACK_TYPE = "application/x-msgpack";

const response = await fetch(url);
const contentType = response.headers.get("Content-Type");
if (contentType && contentType.startsWith(MSGPACK_TYPE) && response.body != null) {
  const object = await decodeAsync(response.body);
  // do something with object
} else { /* handle errors */ }

decodeArrayStream(stream: ReadableStreamLike<ArrayLike<number> | BufferSource>, options?: DecodeAsyncOptions): AsyncIterable<unknown>

It is alike to decodeAsync(), but only accepts a stream that includes an array of items, and emits a decoded item one by one.

for example:

import { decodeArrayStream } from "@msgpack/msgpack";

const stream: AsyncIterator<Uint8Array>;

// in an async function:
for await (const item of decodeArrayStream(stream)) {

decodeMultiStream(stream: ReadableStreamLike<ArrayLike<number> | BufferSource>, options?: DecodeAsyncOptions): AsyncIterable<unknown>

It is alike to decodeAsync() and decodeArrayStream(), but the input stream must consist of multiple MessagePack-encoded items. This is an asynchronous variant for decodeMulti().

In other words, it could decode an unlimited stream and emits a decoded item one by one.

for example:

import { decodeMultiStream } from "@msgpack/msgpack";

const stream: AsyncIterator<Uint8Array>;

// in an async function:
for await (const item of decodeMultiStream(stream)) {

This function is available since v2.4.0; previously it was called as decodeStream().

Reusing Encoder and Decoder instances

Encoder and Decoder classes is provided for better performance:

import { deepStrictEqual } from "assert";
import { Encoder, Decoder } from "@msgpack/msgpack";

const encoder = new Encoder();
const decoder = new Decoder();

const encoded: Uint8Array = encoder.encode(object);
deepStrictEqual(decoder.decode(encoded), object);

According to our benchmark, reusing Encoder instance is about 20% faster than encode() function, and reusing Decoder instance is about 2% faster than decode() function. Note that the result should vary in environments and data structure.

Extension Types

To handle MessagePack Extension Types, this library provides ExtensionCodec class.

Here is an example to setup custom extension types that handles Map and Set classes in TypeScript:

import { encode, decode, ExtensionCodec } from "@msgpack/msgpack";

const extensionCodec = new ExtensionCodec();

// Set<T>
const SET_EXT_TYPE = 0 // Any in 0-127
  type: SET_EXT_TYPE,
  encode: (object: unknown): Uint8Array | null => {
    if (object instanceof Set) {
      return encode([...object]);
    } else {
      return null;
  decode: (data: Uint8Array) => {
    const array = decode(data) as Array<unknown>;
    return new Set(array);

// Map<T>
const MAP_EXT_TYPE = 1; // Any in 0-127
  type: MAP_EXT_TYPE,
  encode: (object: unknown): Uint8Array => {
    if (object instanceof Map) {
      return encode([...object]);
    } else {
      return null;
  decode: (data: Uint8Array) => {
    const array = decode(data) as Array<[unknown, unknown]>;
    return new Map(array);

const encoded = encode([new Set<any>(), new Map<any, any>()], { extensionCodec });
const decoded = decode(encoded, { extensionCodec });

Not that extension types for custom objects must be [0, 127], while [-1, -128] is reserved for MessagePack itself.

ExtensionCodec context

When using an extension codec, it may be necessary to keep encoding/decoding state, to keep track of which objects got encoded/re-created. To do this, pass a context to the EncodeOptions and DecodeOptions (and if using typescript, type the ExtensionCodec too). Don't forget to pass the {extensionCodec, context} along recursive encoding/decoding:

import { encode, decode, ExtensionCodec } from "@msgpack/msgpack";

class MyContext {
  track(object: any) { /*...*/ }

class MyType { /* ... */ }

const extensionCodec = new ExtensionCodec<MyContext>();

// MyType
const MYTYPE_EXT_TYPE = 0 // Any in 0-127
  encode: (object, context) => {
    if (object instanceof MyType) {
      context.track(object); // <-- like this
      return encode(object.toJSON(), { extensionCodec, context });
    } else {
      return null;
  decode: (data, extType, context) => {
    const decoded = decode(data, { extensionCodec, context });
    const my = new MyType(decoded);
    context.track(my); // <-- and like this
    return my;

// and later
import { encode, decode } from "@msgpack/msgpack";

const context = new MyContext();

const encoded = = encode({myType: new MyType<any>()}, { extensionCodec, context });
const decoded = decode(encoded, { extensionCodec, context });

Handling BigInt with ExtensionCodec

This library does not handle BigInt by default, but you can handle it with ExtensionCodec like this:

import { deepStrictEqual } from "assert";
import { encode, decode, ExtensionCodec } from "@msgpack/msgpack";

const BIGINT_EXT_TYPE = 0; // Any in 0-127
const extensionCodec = new ExtensionCodec();
    type: BIGINT_EXT_TYPE,
    encode: (input: unknown) => {
        if (typeof input === "bigint") {
            if (input <= Number.MAX_SAFE_INTEGER && input >= Number.MIN_SAFE_INTEGER) {
                return encode(parseInt(input.toString(), 10));
            } else {
                return encode(input.toString());
        } else {
            return null;
    decode: (data: Uint8Array) => {
        return BigInt(decode(data));

const value = BigInt(Number.MAX_SAFE_INTEGER) + BigInt(1);
const encoded: = encode(value, { extensionCodec });
deepStrictEqual(decode(encoded, { extensionCodec }), value);

The temporal module as timestamp extensions

There is a proposal for a new date/time representations in JavaScript:

This library maps Date to the MessagePack timestamp extension by default, but you can re-map the temporal module (or Temporal Polyfill) to the timestamp extension like this:

import { Instant } from "@std-proposal/temporal";
import { deepStrictEqual } from "assert";
import {
} from "@msgpack/msgpack";

const extensionCodec = new ExtensionCodec();
  type: EXT_TIMESTAMP, // override the default behavior!
  encode: (input: any) => {
    if (input instanceof Instant) {
      const sec = input.seconds;
      const nsec = Number(input.nanoseconds - BigInt(sec) * BigInt(1e9));
      return encodeTimeSpecToTimestamp({ sec, nsec });
    } else {
      return null;
  decode: (data: Uint8Array) => {
    const timeSpec = decodeTimestampToTimeSpec(data);
    const sec = BigInt(timeSpec.sec);
    const nsec = BigInt(timeSpec.nsec);
    return Instant.fromEpochNanoseconds(sec * BigInt(1e9) + nsec);

const instant = Instant.fromEpochMilliseconds(Date.now());
const encoded = encode(instant, { extensionCodec });
const decoded = decode(encoded, { extensionCodec });
deepStrictEqual(decoded, instant);

This will be default once the temporal module is standardizied, which is not a near-future, though.

Decoding a Blob

Blob is a binary data container provided by browsers. To read its contents, you can use Blob#arrayBuffer() or Blob#stream(). Blob#stream() is recommended if your target platform support it. This is because streaming decode should be faster for large objects. In both ways, you need to use asynchronous API.

async function decodeFromBlob(blob: Blob): unknown {
  if (blob.stream) {
    // Blob#stream(): ReadableStream<Uint8Array> (recommended)
    return await decodeAsync(blob.stream());
  } else {
    // Blob#arrayBuffer(): Promise<ArrayBuffer> (if stream() is not available)
    return decode(await blob.arrayBuffer());

MessagePack Specification

This library is compatible with the "August 2017" revision of MessagePack specification at the point where timestamp ext was added:

  • str/bin separation, added at August 2013
  • extension types, added at August 2013
  • timestamp ext type, added at August 2017

The livinng specification is here:


Note that as of June 2019 there're no official "version" on the MessagePack specification. See https://github.com/msgpack/msgpack/issues/195 for the discussions.

MessagePack Mapping Table

The following table shows how JavaScript values are mapped to MessagePack formats and vice versa.

Source Value MessagePack Format Value Decoded
null, undefined nil null (*1)
boolean (true, false) bool family boolean (true, false)
number (53-bit int) int family number (53-bit int)
number (64-bit float) float family number (64-bit float)
string str family string
ArrayBufferView bin family Uint8Array (*2)
Array array family Array
Object map family Object (*3)
Date timestamp ext family Date (*4)
  • *1 Both null and undefined are mapped to nil (0xC0) type, and are decoded into null
  • *2 Any ArrayBufferViews including NodeJS's Buffer are mapped to bin family, and are decoded into Uint8Array
  • *3 In handling Object, it is regarded as Record<string, unknown> in terms of TypeScript
  • *4 MessagePack timestamps may have nanoseconds, which will lost when it is decoded into JavaScript Date. This behavior can be overridden by registering -1 for the extension codec.


This is a universal JavaScript library that supports major browsers and NodeJS.


  • ES5 language features
  • ES2018 standard library, including:
    • Typed arrays (ES2015)
    • Async iterations (ES2018)
    • Features added in ES2015-ES2018

ES2018 standard library used in this library can be polyfilled with core-js.

If you support IE11, import core-js in your application entrypoints, as this library does in testing for browsers.


NodeJS v10 is required, but NodeJS v12 or later is recommended because it includes the V8 feature of Improving DataView performance in V8.

NodeJS before v10 will work by importing @msgpack/msgpack/dist.es5+umd/msgpack.

TypeScript Compiler / Type Definitions

This module requires type definitions of AsyncIterator, SourceBuffer, whatwg streams, and so on. They are provided by "lib": ["ES2021", "DOM"] in tsconfig.json.

Regarding the TypeScript compiler version, only the latest TypeScript is tested in development.


Run-time performance is not the only reason to use MessagePack, but it's important to choose MessagePack libraries, so a benchmark suite is provided to monitor the performance of this library.

V8's built-in JSON has been improved for years, esp. JSON.parse() is significantly improved in V8/7.6, it is the fastest deserializer as of 2019, as the benchmark result bellow suggests.

However, MessagePack can handles binary data effectively, actual performance depends on situations. You'd better take benchmark on your own use-case if performance matters.

Benchmark on NodeJS/v12.18.3 (V8/7.8)

operation op ms op/s
buf = Buffer.from(JSON.stringify(obj)); 840700 5000 168140
buf = JSON.stringify(obj); 1249800 5000 249960
obj = JSON.parse(buf); 1648000 5000 329600
buf = require("msgpack-lite").encode(obj); 603500 5000 120700
obj = require("msgpack-lite").decode(buf); 315900 5000 63180
buf = require("@msgpack/msgpack").encode(obj); 945400 5000 189080
obj = require("@msgpack/msgpack").decode(buf); 770200 5000 154040
buf = /* @msgpack/msgpack */ encoder.encode(obj); 1162600 5000 232520
obj = /* @msgpack/msgpack */ decoder.decode(buf); 787800 5000 157560

Note that Buffer.from() for JSON.stringify() is necessary to emulate I/O where a JavaScript string must be converted into a byte array encoded in UTF-8, whereas MessagePack's encode() returns a byte array.


NPM / npmjs.com

The NPM package distributed in npmjs.com includes both ES2015+ and ES5 files:

  • dist/ is compiled into ES2019 with CommomJS, provided for NodeJS v10
  • dist.es5+umd/ is compiled into ES5 with UMD
    • dist.es5+umd/msgpack.min.js - the minified file
    • dist.es5+umd/msgpack.js - the non-minified file
  • dist.es5+esm/ is compiled into ES5 with ES modules, provided for webpack-like bundlers and NodeJS's ESM-mode

If you use NodeJS and/or webpack, their module resolvers use the suitable one automatically.

CDN / unpkg.com

This library is available via CDN:

<script crossorigin src="https://unpkg.com/@msgpack/msgpack"></script>

It loads MessagePack module to the global object.

Deno Support

You can use this module on Deno.

See example/deno-*.ts for examples.

deno.land/x is not supported yet.



For simple testing:

npm run test

Continuous Integration

This library uses Travis CI.

test matrix:

  • TypeScript targets
    • target=es2019 / target=es5
  • JavaScript engines
    • NodeJS, browsers (Chrome, Firefox, Safari, IE11, and so on)

See test:* in package.json and .travis.yml for details.

Release Engineering

# run tests on NodeJS, Chrome, and Firefox
make test-all

# edit the changelog

# bump version
npm version patch|minor|major

# run the publishing task
make publish

Updating Dependencies

npm run update-dependencies


Copyright 2019 The MessagePack community.

This software uses the ISC license:


See LICENSE for details.