Napping Peanut Monsters


    1.0.0 • Public • Published


    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, [callbacks])
    • Cryo.parse(string, [callbacks])
    var Cryo = require('cryo');
    var obj = {
      name: 'Hunter',
      created: new Date(),
      hello: function() {
        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!

    More powerful JSON


    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!

    Custom Types

    Cryo can allow you to stringify and parse custom types by using the optional callbacks argument. The prepare for stringify is called before each item is stringified, allowing you to alter an object just before it's serialized. The finalize 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, { prepare: 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, { finalize: 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

    Controlling Serialization

    By default, all own properties of an object will be serialized. However, you can specify a custom isSerializable method as part of callbacks to pass to stringify to change this behavior. By default it is defined as such:

    Cryo.stringify(data, { isSerializable: function(item, key) {
      return item.hasOwnProperty(key);


    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

    Stringified Output

    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


    npm i cryonic

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