Simple State-Observer in JavaScript

prop-state.js

/**
 * Simple State-Observer in JavaScript
 */
var PropState = function () {
    var _self = this;
    var _state = {};
    var _callbacks = {};
    if (arguments.length) {
        for (var i in arguments) {
            var obj = arguments[i];
            if (obj.name && obj.value) {
                _state[obj.name] = obj.value;
                _callbacks[obj.name] = obj.onChange;
                (function (propName) {
                    Object.defineProperty(_self, propName, {
                        get: function () {
                            return _state[propName];
                        },
                        set: function (value) {
                            var oldValue = _state[propName];
                            _state[propName] = value;
                            if (value !== oldValue) {
                                _self.onChange(_state, propName, value);
                                if (typeof _callbacks[propName] === 'function') {
                                    _callbacks[propName](propName, value);
                                }
                            }
                        },
                        enumerable: true,
                        configurable: false,
                    });
                })(obj.name);
            }
        }
    }
};
Object.defineProperty(PropState.prototype, 'onChange', {
    value: function (state, key, value) {},
    writable: true,
    enumerable: false,
    configurable: false,
});

usage-example.js

// define global state change callback
PropState.prototype.onChange = function (state, key, value) {
    console.log('Object State updated ', state);
};

// initialize all states
var propState = new PropState(
    {name: 'a', value: 1, onChange: function (key, value) { console.log(key+' updated', value); }},
    {name: 'b', value: 2, onChange: function (key, value) { console.log(key+' updated', value); }},
    {name: 'c', value: 3}
);

console.log(propState.a);

propState.a = 3; // change state to invoke its callback

console.log(propState.a);

// get all states
for (var stateName in propState) {
    console.log(propState[stateName]);
}