Disable unknown variable in function [duplicate]

Question

function Shape(X,Y) {
    this.X = X;
    this.Y= Y;
}

function Rectangle(Name,Desc,X,Y) {
    Shape.call(this, X, Y);
    this.Name = Name;
    this.Desc = Desc;
}

var Z = new Rectangle('Rectangle', '',25,25);
Z.ABC = '123';

The problem is, the Z.ABC is not the variable under the function Shape and Rectangle, it should hit error because ABC is not the variable under shape and rectangle function.

How to disable unknown variable, not allow to declare unknown variable outside the function ?

Answer 1

You can call Object.preventExtensions on your object after constructing it and adding all the properties that you want. You won't be able to create new properties on the object then.

"use strict";
function Shape(X,Y) {
    this.X = X;
    this.Y= Y;
}

function Rectangle(Name,Desc,X,Y) {
    Shape.call(this, X, Y);
    this.Name = Name;
    this.Desc = Desc;
}

var Z = Object.preventExtensions(new Rectangle('Rectangle', '',25,25));
Z.ABC = '123'; // Uncaught TypeError: Cannot add property ABC, object is not extensible

Answer 2

To prevent assignment operations to your objects you can "freeze" them. Reference

function Shape(X,Y) {
    this.X = X;
    this.Y= Y;
}

function Rectangle(Name,Desc,X,Y) {
    Shape.call(this, X, Y);
    this.Name = Name;
    this.Desc = Desc;
}

var Z = new Rectangle('Rectangle', '',25,25);
Object.freeze(Z);
Z.ABC = '123';
console.log(Z);