Question

I have read that Javascript’s inheritance is prototypal.What does it mean?How can an object defined by the programer inherit the properties of a predefined object such as window ?
For example I need the function eval() in my own class . How can it be achieved?

Answer 1

What do you want exactly echieve to?
Here is the simplest way (not the best) of prototype inheritance:

var obj1=new Object1Constructor();
var obj2=new Object2Constructor();

obj2.prototype=obj1;

It means that obj1 inherits all properties of obj2

I’ve forgot the main thing: eval==evil;

UPDATE:
I’ve made mistakes in the code above. That is not inheritance. Here is updated code:

var Object1Constructor=function(){ // one object constuctor
    //properties definition goes here
}

var Object2Constructor=function(){ // another object constuctor
    //properties definition goes here
}

Object2Constructor.prototype=new Object1Constructor();

var obj=new Object2Constructor();

And that is inharitance. Now obj has properties defined in Object2Constructor and Object1Constructor – parent ‘class’.
See CMS’s comment below. He is totally right.