Immutable Data Structures: A New Feature in ECMAScript 2024

ECMAScript 2024 introduces several exciting updates, but one feature that stands out to me is the introduction of Immutable Data Structures. These new structures—Records and Tuples—are game-changers for managing data in JavaScript. They offer a satisfying way of keeping our data sound, secure, and consistent, which is of the utmost importance when we want reliable applications that we can easily maintain. Here’s why immutable data structures are so exciting, and how you can use them most effectively.

What Are Records and Tuples?

Records and Tuples are new data structures that are immutable by design. This means that once you create a Record or Tuple, its contents cannot be changed. Any attempt to modify them results in a new instance being created, while the original remains unchanged. This immutability helps prevent unintended side effects and makes your code more predictable.

Why Use Immutable Data Structures?

• Predictability: Immutable data structures make it easier to reason about your code because you know that once data is set, it won't be changed accidentally elsewhere in your application.
• Debugging: With immutability, you avoid issues related to data being modified unexpectedly, making debugging simpler.
• Functional Programming: Immutable data fits well with functional programming paradigms, where functions avoid side effects and data is treated as immutable.

Creating and Using Records

Records are like immutable objects. They are defined with a set structure and cannot be altered after creation. Here’s a quick look at how to use Records:

// Creating an immutable Record const kittyFacts = 
#{ name: "Turbodog", age: 17, favoriteToy: "Laser Pointer" }; 
// Accessing values 
console.log(kittyFacts.name); 
// Outputs: Turbodog 
console.log(kittyFacts.favoriteToy); 
// Outputs: Laser Pointer 
// Attempting to modify will create a new instance 
const updatedKittyFacts = #{ ...kittyFacts, age: 18 };
console.log(kittyFacts.age); 
// Outputs: 17 (unchanged) 
console.log(updatedKittyFacts.age); 
// Outputs: 18 (new instance)

In this example, kittyFacts is an immutable Record. Any modifications to it, such as updating the age, result in a new updatedKittyFacts Record, leaving the original kittyFacts intact.

Working with Tuples

Tuples are immutable arrays that can hold a fixed number of elements. They are particularly useful for representing ordered collections of values that shouldn't be altered.

// Creating an immutable Tuple 
const concertSetlist = #[ "Tupelo", "Live Oak", "Strawberry Woman", "Elephant" ]; 
// Accessing values 
console.log(concertSetlist[0]);
 // Outputs: Tupelo 
console.log(concertSetlist[2]);
 // Outputs: Strawberry Woman 
// Attempting to modify will create a new instance
 const updatedSetlist = #[...concertSetlist, "Chaos and Clothes"]; 
console.log(concertSetlist.length); 
 // Outputs: 4 (unchanged) 
console.log(updatedSetlist.length);
// Outputs: 5 (new instance)

; // Accessing values console.log(concertSetlist[0]); // Outputs: Tupelo console.log(concertSetlist[2]); // Outputs: Strawberry Woman // Attempting to modify will create a new instance const updatedSetlist = #[...concertSetlist, "Chaos and Clothes"]; console.log(concertSetlist.length); // Outputs: 4 (unchanged) console.log(updatedSetlist.length); // Outputs: 5 (new instance)

Here, concertSetlist is an immutable Tuple. Adding a new song to the setlist creates a new updatedSetlist Tuple, preserving the original.

Advanced Operations with Records and Tuples

Records and Tuples come with useful methods for handling data immutably. For example, the with method for Tuples allows for easy updates at specific indices:

// Creating a Tuple 
const originalMixtape = #[ "If We Were Vampires", "World Leader Pretend", "Right Back to It" ];
 // Updating a specific index 
const updatedMixtape = originalMixtape.with(1, "Turn You Inside-Out"); 
console.log(originalMixtape); 
// Outputs: #[ "If We Were Vampires", "World Leader Pretend", "Right Back to It" ]; 
console.log(updatedMixtape); 
// Outputs: #[ "If We Were Vampires", "Turn You Inside-Out", "Right Back to It" ];

// Creating a Tuple const originalMixtape = #

; // Updating a specific index const updatedMixtape = originalMixtape.with(1, "Turn You Inside-Out"); console.log(originalMixtape); // Outputs: #

; console.log(updatedMixtape); // Outputs: #

;

In this example, the with method updates the track at index 1 without altering the original originalMixtape.

Conclusion

Immutable data structures—Records and Tuples— were introduced in ECMAScript 2024, and represent a major improvement for JavaScript. They help promote data consistency, simplify debugging, and align well with functional programming practices. By experimenting with these immutable structures, you can create more reliable and maintainable applications while avoiding the common surprises and side effects of mutable data.

sources:

https://www.interactivated.me/blog/whats-new-in-javascript-top-10-exciting-features-for-2024

https://thenewstack.io/whats-new-for-javascript-developers-in-ecmascript-2024/

https://www.w3schools.com/js/js_2024.asp

https://github.com/tc39/proposal-record-tuple

https://tc39.es/proposal-record-tuple/tutorial/