For every object we create in javascript the javascript engine creates a hidden class for it.Which contains properties and poperty attributes. llike offset,enumerable,writable etc. My question is why does javascript use hidden classes.

var x=new obj(2);//Assume we create a new obj with a proerty a initialized with 2; so var x contains the reference address of the object and we can access the property by adding required offset to the reference address. So why do we need hidden class?