javascript: disable re-writing object methods

Question

Is there any way to disable the rewriting on methods on javascript objects?

For example :

var myObj=new Object();
myObj.doSomething=function(){
 alert("good message")
}

myObj.doSomething=function(){
 alert("bad message")
}

myObj.doSomething(); // I want to alert me with "good message"

I think this can be done , cause I wanted to to rewrite a method a few years ago, and I received an error in javascript console about that method has only get and not set.

Thanks

Answer 1

In ECMAScript 5 you can set objects to be unmodifiable :

Object.freeze(myObj);

You can create an individual property that can't be modified using:

Object.createProperty(myObj, 'name', descriptor);

where descriptor is itself an object containing flags , one of which is configurable which if set to false prevents that property from being changed or deleted.

Answer 2

JavaScript is designed around the notion that anything can be changed. You can override the functionality of just about anything , anywhere , at any time.

This is both a blessing and a curse.

If you ran into that error message, it was likely either (a) a bug in a JavaScript/JScript implementation, or (b) not what you thought it was.

AMMENDED: It's possible you were looking at ECMAScript 5 code. I've been maintaining ECMAScript 3 for so long I've apparently developed cataracts that blind me to that possibility. Forgive me. I stand humbly corrected.

Answer 3

While Alnitak has a nice direct answer to your question, depending on what you are trying to accomplish you may be able to prevent 're-writing' a method by making it a 'private' variable through a closure. It won't protect 'public' functions, but can hide private ones and prevent them from being modified.

var myObj = (function(){
    var data = {count: 0};
    var privateFunction1 = function(){
      data.count++;
    };

    var privateFunction2 = function(){
      // do something else
    };

    var result = {
        callPrivateFunction: function(){
            privateFunction();
            privateFunction2();
        }
    };

    return result;
})();

Of course, any public function that calls the private function is re-writable, so depending on what you're trying to accomplish the may just be pushing the problem around. However, this approach is a nice way to accomplish some encapsulation and not present more in the API of the object than you want.