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Object.freeze: Immutable Objects

By David Walsh on September 10, 2018

One of my favorite part of JavaScript has always been mutability of objects. I loved that MooTools and likewise frameworks could modify native prototypes to enhance them with functionality we knew the language need; in fact, I credit MooTools with pushing the web forward.

There are cases, however, where you don't want an object to be modifiable; you don't want values for existing properties to be changed, added, or removed. That's where Object.freeze can help -- with Object.freeze you can create immutable objects you can trust!

const obj = Object.freeze({
    x: 1,
    y: 2
});

// None of these do anything
obj.x = 8; // { x: 1, y: 2}
delete obj.x; // { x: 1, y: 2}
obj.z = 3;  // { x: 1, y: 2}

Object.freeze is a welcomed addition to JavaScript and a necessary one. If you have objects whose integrity you want to secure, immutability is required. Object.seal provides similar functionality without the ability to freeze values, so Object.freeze is your best choice when you want to lock down an object!

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Discussion

Shallow
It’s good to remind that Object.freeze does only shallow freeze.
Varghese
That’s a nice feature. Much needed. However, I hope the browser support is good.
MaxArt
Should I remind that MooTools’ practice to extend native prototypes prevented W3C to use well-known names like contains and flatten, because it would have literally broken the web?
Extending native prototypes is the last thing you’d want in a general purpose library.

Object.freeze: Immutable Objects

Recent Features

Create a CSS Flipping Animation

Designing for Simplicity

Incredible Demos

Create Tiny URLs with TinyURL, MooTools, and PHP

Reverse Element Order with CSS Flexbox

Discussion