gistfile1.js

/**
 * Registering callbacks on property setters.
 */
for(var prop in object){
  // Ignore functions
  if(typeof object[prop] !== 'function'){
    (function(obj, attr) {
      // If object does not already have a getter
      if (!object.__lookupGetter__(prop)) {
        // This variable will hold the value of the property
        var value = obj[attr];
        // Define the setter which will invoke the callbacks.
        obj.__defineSetter__(attr, function(v) {
          // Call all registered callbacks
          ObjectObserver._getCallbacks(obj).each(function(method){
            method(obj, attr, v);
          });
          value = v;
        });
        // Define corresponding getter
        obj.__defineGetter__(attr, function() {
          return value;
        });
      }
    })(object, prop);
  }
}