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Encode and parse data in the Concise Binary Object Representation (CBOR) data format (RFC7049).


$ npm install --save cbor

NOTE This package now requires node.js 4.1 or higher. If you want a version that works with older node.js versions, you can install like this:

npm install 'hildjj/node-cbor#node0' --save


See the full API documentation.

From the command line:

$ bin/json2cbor package.json > package.cbor
$ bin/cbor2json package.cbor
$ bin/cbor2diag package.cbor


var cbor = require('cbor');
var assert = require('assert');
var encoded = cbor.encode(true); // returns <Buffer f5> 
cbor.decodeFirst(encoded, function(error, obj) {
  // error != null if there was an error 
  // obj is the unpacked object 
  assert.ok(obj === true);
// Use integers as keys? 
var m = new Map();
m.set(1, 2);
encoded = cbor.encode(m); // <Buffer a1 01 02> 

Allows streaming as well:

var cbor = require('cbor');
var fs = require('fs');
var d = new cbor.Decoder();
d.on('data', function(obj){
var s = fs.createReadStream('foo');
var d2 = new cbor.Decoder({input: '00', encoding: 'hex'});
d.on('data', function(obj){

There is also support for synchronous decodes:

try {
  console.log(cbor.decodeFirstSync('02')); // 2 
  console.log(cbor.decodeAllSync('0202')); // [2, 2] 
} catch (e) {
  // throws on invalid input 

The sync encoding and decoding are exported as a leveldb encoding, as cbor.leveldb.

Supported types

The following types are supported for encoding:

  • boolean
  • number (including -0, NaN, and ±Infinity)
  • string
  • Array, Set (encoded as Array)
  • Object (including null), Map
  • undefined
  • Buffer
  • Date,
  • RegExp
  • url.URL
  • bignumber

Decoding supports the above types, including the following CBOR tag numbers:

Tag Generated Type
0 Date
1 Date
2 bignumber
3 bignumber
4 bignumber
5 bignumber
32 url.URL
35 RegExp

Adding new Encoders

There are several ways to add a new encoder:

encodeCBOR method

This is the easiest approach, if you can modify the class being encoded. Add an encodeCBOR method to your class, which takes a single parameter of the encoder currently being used. Your method should return true on success, else false. Your method may call encoder.push(buffer) or encoder.pushAny(any) as needed.

For example:

class Foo {
  constructor () { = 1
    this.two = 2
  encodeCBOR (encoder) {
    const tagged = new Tagged(64000, [, this.two])
    return encoder.pushAny(tagged)

You can also modify an existing type by monkey-patching an encodeCBOR function onto its prototype, but this isn't recommended.


Sometimes, you want to support an existing type without modification to that type. In this case, call addSemanticType(type, encodeFunction) on an existing Encoder instance. The encodeFunction takes an encoder and an object to encode, for example:

class Bar {
  constructor () {
    this.three = 3
const enc = new Encoder()
enc.addSemanticType(Bar, (encoder, b) => {

Adding new decoders

Most of the time, you will want to add support for decoding a new tag type. If the Decoder class encounters a tag it doesn't support, it will generate a Tagged instance that you can handle or ignore as needed. To have a specific type generated instead, pass a tags option to the Decoder's constructor, consisting of an object with tag number keys and function values. The function will be passed the decoded value associated with the tag, and should return the decoded value. For the Foo example above, this might look like:

const d = new Decoder({tags: { 64000: (val) => {
  // check val to make sure it's an Array as expected, etc. 
  const foo = new Foo() = val[0]
  foo.two = val[1]
  return foo


Get a list of build steps with npm run. I use npm run dev, which rebuilds, runs tests, and refreshes a browser window with coverage metrics every time I save a .coffee file. If you don't want to run the fuzz tests every time, set a NO_GARBAGE environment variable:

env NO_GARBAGE=1 npm run dev

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