Javascript redefine and override existing function body

Question

I am wondering can we still change the function body once it is constructed ?

     var O = function(someValue){
           this.hello = function(){
                 


        

Answer 1

When you access a property, system first looks for it in the instance. If it is not found, it looks for it in the prototype. This is why this.hello is being used, rather than O.prototype.hello.

If you wish to override the implementation of hello, you will need to use JavaScript inheritance. Here is a basic example:

var A = function(){
    console.log("A is getting constructed");
};

A.prototype.constructor = A;
A.prototype.someValue = 1;
A.prototype.hello = function() {
    console.log("A.hello(): " + this.someValue);
};

var B = function(){
    //Constructor of A is automatically called before B's

    console.log("B is getting constructed");
};
B.prototype = new A; //Inherit from A
B.prototype.constructor = B;
B.prototype.hello = function() {
    console.log("B.hello() called");
    console.log("Calling base class method");
    A.prototype.hello.call(this);
};

var a = new A();
a.hello();

var b = new B();
b.hello();