What Are Immutable Operations?

In programming, an object or data structure is termed immutable if its state remains unchanged once created. To modify an immutable object, we generate a new copy with the necessary alterations. Although this may seem like an extra step, there are compelling reasons to utilize immutable objects. For starters, they simplify the reasoning behind program behavior since we can be assured that once an object is instantiated, it won't unexpectedly change.

Additionally, immutability helps avoid unintentional alterations, thereby reducing the likelihood of bugs. Moreover, since immutable objects do not require in-place updates, they can often result in better performance compared to their mutable counterparts.

Practical Approaches to Immutable Operations in JavaScript

While JavaScript lacks native support for complete immutability, we can still leverage its advantages. Several libraries, like immutable.js and immer, assist in managing immutable data structures. However, even without these tools, we can adopt best practices to foster immutability in our code. Here are some strategies to begin with:

Array Methods for New Arrays

When dealing with arrays, several methods return new arrays rather than modifying the original. These include filter(), map(), reduce(), and others. By chaining method calls on an initial array, we can create entirely new arrays based on the original data without making changes to it.

For instance, to convert every string in an array to uppercase:

const arr = ['apple', 'banana', 'carrot'];

const uppercasedArr = arr.map((str) => str.toUpperCase());

console.log(arr); // logs: ['apple', 'banana', 'carrot']

console.log(uppercasedArr); // logs: ['APPLE', 'BANANA', 'CARROT']

In this example, calling map() returns a new array containing the transformed strings while leaving the original intact.

Utilizing Object.freeze()

For those looking to ensure an object remains truly immutable, Object.freeze() can be employed to prevent further modifications. Once an object is frozen, no new properties can be added, removed, or modified, even in nested objects. However, it's important to note that this only safeguards against direct manipulation; other parts of the code may still refer to mutable versions of its contents.

Here's an example:

const obj = {foo: 1, bar: []};

Object.freeze(obj);

// Attempted modifications below will either fail silently or throw errors

obj.foo = 2; // fails silently

obj.bar.push(3); // modifies 'bar', despite being frozen!

obj.qux = 4; // fails silently

console.log(obj); // logs: {foo: 1, bar: [3]}

While Object.freeze() provides some level of protection against unwanted changes, it doesn't guarantee complete safety due to potential shared references elsewhere in the application.