serializable.js

/**
 *  The Serializable module adds a set of handy utilities to make it easier to
 *  work with JSON-serialized classes.
 *
 *  Usage: 
 *  
 *    function MyClass(serialized_data) {
 *      this.init({
 *        name: 'default name'  
 *      }, serialized_data);
 *    };
 *
 *    MyClass.prototype.print_name = function() {
 *      puts("The name of the instance(" + this.type + ") is: " + this.name);
 *    }
 *
 *    Serializable.make(MyClass, 'MyClass');
 *
 *    var instance = new MyClass();
 *    var data = instance.strinifigy();
 *    var instance2 = Serializable.parse(data);
 *    instance2.print_name();
 */
var Serializable = {

  // Cache for serializable classes.
  _classes: {},
  
  /**
   *  Generates a TypeError exception.
   */
  TypeError: function(name) {
    return function() {
      throw "Error parsing object: Could not match type: " + name;
    }
  },

  /**
   *  Take's a class and make it serializable. Specifiy the type_name to make
   *  the Class instanceable from the Serializable.parse function. 
   */
  make: function(Class, type_name) {
    
    // Adds a serialize init method to the class's prototype base. The method
    // takes a dict of default values and a dict of user-defined values. The
    // user-defined values are prioritized. The init method MUST be called in 
    // the Class constructor.  
    Class.prototype.init = function(defaults, props) {
      var v = props || {};
      this._defaults = defaults;
      for (var name in defaults) {
        this[name] = v[name] || defaults[name];
      }
      this['type'] = type_name;
    }
    
    // Adds a serialize strinifigy method to the specified class prototype. The
    // method converts the object into a JSON string. All instance properties 
    // in the _props arguments is serialized. Leave the argument blank to
    // serialize all predefined (defaults) properties.
    Class.prototype.stringify = function(_props) {
      var props = _props || Serializable.get_names_from_dict(this._defaults);
      var length = props.length, obj = {};
      while (length--) {
        var prop = props[length];
        obj[prop] = this[prop];
      }
      return JSON.stringify(obj);
    }
    
    if (type_name) Serializable._classes[type_name] = Class;
  },
  
  /**
   *  Parse's a JSON string and then create's an Class instance based on the 
   *  type property
   */
  parse: function(json) {
    var props = JSON.parse(json);
    var t = props.type;
    var Class = Serializable._classes[t] || Serializable.TypeError(t);
    return new Class(props);
  },
  
  /**
   *  Takes a dict and returns all property names in an array.
   */
  get_names_from_dict: function(dict) {
    var result = [];
    for (var name in dict) {
      result.push(name);
    }
    return result;
  }
}