Calling base method using javascript prototype

Question

Is it possible to call the base method from a prototype method in javascript if it's been overridden?

MyClass = function(name){

    this.name = name;

    this.do = function(){ //do somthing };

};

MyClass.prototype.do = function(){  

    if (this.name === 'something'){

        //do something new

    }else{
        //CALL BASE METHOD
    }

};

Answer 1

I did not understand what exactly you're trying to do, but normally implementing object-specific behaviour is done along these lines:

function MyClass(name) {
    this.name = name;
}

MyClass.prototype.doStuff = function() {
    // generic behaviour
}

var myObj = new MyClass('foo');

var myObjSpecial = new MyClass('bar');
myObjSpecial.doStuff = function() {
    // do specialised stuff
    // how to call the generic implementation:
    MyClass.prototype.doStuff.call(this /*, args...*/);
}

Answer 2

If I understand correctly, you want Base functionality to always be performed, while a piece of it should be left to implementations.

You might get helped by the 'template method' design pattern.

Base = function() {}
Base.prototype.do = function() { 
    // .. prologue code
    this.impldo(); 
    // epilogue code 
}
// note: no impldo implementation for Base!

derived = new Base();
derived.impldo = function() { /* do derived things here safely */ }

Answer 3

Well one way to do it would be saving the base method and then calling it from the overriden method, like so

MyClass.prototype._do_base = MyClass.prototype.do;
MyClass.prototype.do = function(){  

    if (this.name === 'something'){

        //do something new

    }else{
        return this._do_base();
    }

};

Answer 4

I'm afraid your example does not work the way you think. This part:

this.do = function(){ /*do something*/ };

overwrites the definition of

MyClass.prototype.do = function(){ /*do something else*/ };

Since the newly created object already has a "do" property, it does not look up the prototypal chain.

The classical form of inheritance in Javascript is awkard, and hard to grasp. I would suggest using Douglas Crockfords simple inheritance pattern instead. Like this:

function my_class(name) {
    return {
        name: name,
        do: function () { /* do something */ }
    };
}

function my_child(name) {
    var me = my_class(name);
    base_do = me.do;
    me.do = function () {
        if (this.name === 'something'){
            //do something new
        } else {
            base_do();
        }
    }
    return me;
}

var o = my_child("something");
o.do(); // does something new

var u = my_child("something else");
u.do(); // uses base function

In my opinion a much clearer way of handling objects, constructors and inheritance in javascript. You can read more in Crockfords Javascript: The good parts.

Answer 5

No, you would need to give the do function in the constructor and the do function in the prototype different names.