Javascript
JavaScript Fundamentals -- Objects in JavaScript

Freezing Objects

PRO

There are times when you don't want the data in your object to change, but unfortunately JavaScript will let you change the vaue of a key on an object at any time, even if you use the const keyword. Luckily, there's a built in Object class (similar to Math like we talked about before) that provides a method called freeze that will help make it so the object and its data is read only. But for it to work, you first need to put the file in strict mode:

'use strict';

// File contents

After that, you can call the freeze method and pass in an object:

'use strict';

const dog = {
    name: 'Max'
}

Object.freeze(dog);

Now that the object is frozen, we can't change the value of any key or add a key to the object:

dog.name = 'Duke'; // Error Cannot assign to read only property 'name' of object
dog.age = 3; // Error Cannot add property age, object is not extensible

This will work in most situations, except if you try and reassign the entire value of the variable to a new object. If your object is declared with the let keyword, you could reassign its value to a new object, even if it's frozen. However, if you use const, JavaScript prevents that as well. So if you use const and Object.freeze together, your objects should be protected pretty well.

You can read more about this in this blog post.