Easily pickle/serialize/freeze/store and re-hydrate complex JavaScript objects (including Functions)


JSON on steroids.

Built for node.js and browsers. Cryo is inspired by Python's pickle and works similarly to JSON.stringify() and JSON.parse(). Cryo.stringify() and Cryo.parse() improve on JSON in these circumstances:

$ npm install cryo

With Bower:

bower install cryo

Add the latest minified build to your project as a script:

<script type='text/javascript' src='cryo-0.0.4.js'></script>

Cryo has a very simple API that mimicks JSON:

  • Cryo.stringify(item, [callback])
  • Cryo.parse(string, [callback])
var Cryo = require('cryo');
var obj = {
  name: 'Hunter',
  created: new Date(),
  hellofunction() {
    console.log( + ' said hello in ' + this.created.getFullYear() + '!');
var frozen = Cryo.stringify(obj);
var hydrated = Cryo.parse(frozen);
hydrated.hello(); // Hunter said hello in 2013! 

Cryo takes a verbatim snapshot of all your properties, including those that are undefined - which JSON ignores.

var Cryo = require('../lib/cryo');
var obj = {
  defaultValue: undefined
var withJSON = JSON.parse(JSON.stringify(obj));
console.log(withJSON.hasOwnProperty('defaultValue'));   // false 
var withCryo = Cryo.parse(Cryo.stringify(obj));
console.log(withCryo.hasOwnProperty('defaultValue'));   // true 

Cryo successfully works with Date objects, which JSON.stringify() mangles into strings.

var Cryo = require('../lib/cryo');
var now = new Date();
var withJSON = JSON.parse(JSON.stringify(now));
console.log(withJSON instanceof Date);              // false 
var withCryo = Cryo.parse(Cryo.stringify(now));
console.log(withCryo instanceof Date);              // true 

JSON.stringify() makes multiple copies of single objects, losing object relationships. When several references to the same object are stringified with JSON, those references are turned into clones of each other. Cryo maintains object references so the restored objects are identical to the originals. This is easier to understand with an example:

var Cryo = require('../lib/cryo');
var userList = [{ name: 'Abe' }, { name: 'Bob' }, { name: 'Carl' }];
var state = {
  users: userList,
  activeUser: userList[1]
var withJSON = JSON.parse(JSON.stringify(state));
console.log(withJSON.activeUser === withJSON.users[1]);   // false 
var withCryo = Cryo.parse(Cryo.stringify(state));
console.log(withCryo.activeUser === withCryo.users[1]);   // true 

Cryo successfully stringifies and parses Infinity, which JSON mangles into null.

var Cryo = require('../lib/cryo');
var number = Infinity;
var withJSON = JSON.parse(JSON.stringify(number));
console.log(withJSON === Infinity);                 // false 
var withCryo = Cryo.parse(Cryo.stringify(number));
console.log(withCryo === Infinity);                 // true 

Objects, Arrays, Dates, and Functions can all hold properties, but JSON will only stringify properties on Objects. Cryo will recover properties from all containers:

var Cryo = require('../lib/cryo');
function first() {}
first.second = new Date();
first.second.third = [1, 2, 3];
first.second.third.fourth = { name: 'Hunter' };
try {
  var withJSON = JSON.parse(JSON.stringify(first));
  console.log( === 'Hunter');
} catch(e) {
  console.log('error');                                       // error 
var withCryo = Cryo.parse(Cryo.stringify(first));
console.log( === 'Hunter');  // true 

Cryo will stringify functions, which JSON ignores.

Note: Usually, if you've come up with a solution that needs to serialize functions, a better solution exists that doesn't. However, sometimes this can be enormously useful. Cryo will make faithful hydrated functions and objects with properties that are functions.

var Cryo = require('../lib/cryo');
function fn() {
  console.log('Hello, world!');
try {
  var withJSON = JSON.parse(JSON.stringify(fn));
} catch(e) {
  console.log('error');                             // error 
var withCryo = Cryo.parse(Cryo.stringify(fn));
withCryo();                                         // Hello, world! 

Cryo can allow you to stringify and parse custom types by using the optional callback argument. The callback for stringify is called before each item is stringified, allowing you to alter an object just before it's serialized. The callback for parse is called after each item is re-created, allowing you to alter an object just after it's de-serialized:

function Person() {}
var person = new Person();
person.friends = [new Person()];
var stringified = Cryo.stringify(person, function(obj) {
  // store any object's constructor name under a variable called 
  // __class__ which can later be be used to restore the object's 
  // prototype. 
  obj.__class__ =;
var parsed = Cryo.parse(stringified, function(obj) {
  // look for objects that define a __class__ and restore their 
  // prototype by finding the class on the global window (you may need 
  // to look elsewhere for the class). 
  if (obj.__class__ && window[obj.__class__]) {
    obj.__proto__ = window[obj.__class__].prototype;
    delete obj.__class__;
parsed instanceof Person; // true 
parsed.friends[0] instanceof Person; // true 

JSON chokes when you try to stringify an object with a reference to a DOM node, giving Uncaught TypeError: Converting circular structure to JSON. Cryo will ignore DOM nodes so you can serialize such objects without hassle.

var obj = {
  button: document.getElementById('my-button');
  message: 'Hello'
try {
  var withJSON = JSON.parse(JSON.stringify(obj));
  console.log(withJSON.message === 'Hello');
} catch(e) {
  console.log('error');                             // error 
var withCryo = Cryo.parse(Cryo.stringify(obj));
console.log(withCryo.message === 'Hello');          // true 

Cryo.stringify() returns valid JSON data with non-compatible types encoded as strings. Thus, anything you can do with JSON, you can do with Cryo.

Here is the stringified result from the hello, world example:

      "contents": {},
      "contents": {},
      "value":"_CRYO_FUNCTION_function () {\n    console.log( + ' said hello in ' + this.created.getFullYear() + '!');\n  }"

Tests require node.js.

$ git clone git://
$ cd cryo
$ make setup
$ make test