A pure-javascript adaptation of the W3C's structured cloning algorithm, designed to provide an easy interface for deep copying of complex objects

npm install cyclonejs
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Cyclone is an attempt to implement an adaptation of the HTML5 Structured Cloning Algorithm.

It is meant to be:

  • Synchronous
  • Agnostic to the JS environment (doesn't rely on postMessage(), replaceState(), etc), and therefore agnostic to types such as File, Blob, etc (which also allows it to be synchronous in the first place).
  • Serve the majority of use cases out of the box, but also provide a mechanism to be extensible (coming soon).
  • Able to copy functions (including function objects) by reference. This is the only property that's copied by reference. See above about serving the majority of use cases.

It can handle objects containing:

  • Primitives
  • null
  • undefined
  • Number objects
  • String objects
  • Boolean objects
  • Date objects
  • RegExp objects
  • Array objects
  • Object (or "plain") objects
  • In most cases, Objects instantiated with the use of a custom constructor (e.g. function Foo() { = 'baz' }; var cloneable = new Foo();)
  • Cyclic references to itself, including nested cyclic references
  • Cyclic references to objects within itself, including nested cyclic references to those objects
  • Non-enumerable properties, or properties with custom descriptors
  • Accessor properties


This module exposes a single object, CY, into the global scope when used within browsers. A client can then use this module's clone method to perform clone operations.

  var o = {
    date: new Date(),
    number: Math.random()
  o.self = o;
  o.tricky = { self: o };

  var c = CY.clone(o);

  c === o; // false ===; // false

  +( === +(; // true
  c.number === o.number;  // true
  c.self === c;  // true
  c.tricky.self === c;  // true

Note that cycloneJS also supports AMD loading as well as use within nodeJS/CJS environments, so with node you could do something like

var CY = require('cyclonejs');
// Do some CY.clone()-ing

Cloning options

CY.clone takes an options hash as a second argument, which accepts the following parameters:

  • allowFunctions: (default: false) If set to true, CY.clone will simply pass functions through to the copied object, instead of throwing an error saying it can't clone a function.
var fnObject = {
  f: function() {}
var copy = CY.clone(fnObject, {
  allowFunctions: true
console.log(copy.f === fnObject.f) // true
  • suppressErrors: (default: false) If set to true, CY.clone will return null instead of throwing an Error if it comes across an object it doesn't know how to clone. If you need CY.clone to be extremely forgiving, this is the option for you.
var mixedBag = {
  htmlElement: document.createElement('div'),
  ctx: document.getElementsByTagName('canvas')[0].getContext('2d')
var result = CY.clone(mixedBag, {
  suppressErrors: true
console.log(result); // null

Extending CY.clone()'s functionality with defineCloneProcedure

Because cyclone is built to be environment-agnostic, it is incapable of handling certain cloneable host objects, such as DOM elements, out-of-the-box. However, that doesn't mean that these objects themselves aren't cloneable! For example, most DOM elements can be cloned using cloneNode(). Cyclone comes with a method called defineCloneProcedure that allows you to add in your own cloning methods for host objects, or other objects, that can't be handled in a standard way by CY.clone. Here's how you can add support for cloning DOM nodes using CY.clone:

var elementTagRE = /^HTML\w*Element$/;
  detect: function(obj) {
    var klass =, -1);
    return elementTagRE.test(klass) && typeof obj.cloneNode === 'function';
  copy: function(el) {
    return el.cloneNode()

var orig = document.createElement('div');
var clone = CY.clone(orig);
console.log(clone !== orig); // True

Here's another example of how to handle most jQuery objects:

  detect: function(obj) {
    return 'jquery' in obj;
  copy: function($el) {
    return $el.clone();

CY.clone($('#main')); // Returns a cloned jQuery object.

defineCloneProcedure takes an object that must contain two properties detect and copy.

detect should be a function that takes an object and returns true if and only if obj is of the type that you want to define your custom cloning procedure for. In the above example, detect ensures that the [[Class]] of obj is specified as some kind of HTML Element, and that it has a function called cloneNode.

copy should be a function that takes an object and returns a copy of that object. You are responsible for providing the procedure used to copy the object. In the case of an HTML Element, we simply call its cloneNode method.

defineCloneProcedure will return true if the cloning procedure is successfully defined, and false otherwise. Note that defineCloneProcedure gives priority to procedures that were defined most recently. That means if you define two cloning procedures whose detect functions both return true for a given type of object, the latter's copy function will be used.

You can erase all custom cloning procedures defined by calling CY.clearCustomCloneProcedures().


First install the module

$ git clone
$ cd /path/to/cycloneJS
$ npm install .

Then just run npm test within the module's directory whenever you want to test. This will run jshint on all javascript files as well as run tests against cyclone.

Issues and Pull Requests are widely encouraged!!

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