DEV Community πŸ‘©β€πŸ’»πŸ‘¨β€πŸ’»

DEV Community πŸ‘©β€πŸ’»πŸ‘¨β€πŸ’» is a community of 967,911 amazing developers

We're a place where coders share, stay up-to-date and grow their careers.

Create account Log in
Maxi Contieri
Maxi Contieri

Posted on • Updated on • Originally published at maximilianocontieri.com

Code Smell 86 - Mutable Const Arrays

Const declares something to be constant. Can it mutate?

TL;DR: Don't rely on languages cheating about directives.

Problems

  • Unexpected side effects.

  • Accidental complexity.

Solutions

  1. Use better languages

  2. Use spread operator

Sample Code

Wrong

const array = [1, 2];

array.push(3)

//array => [1, 2, 3]
//Wasn't it constant ?
//constant != immutable ?
Enter fullscreen mode Exit fullscreen mode

Right

const array = [1, 2];

const newArray = [...array,3 ]

//array => [1, 2] Didn't mutate
//newArray = [1, 2, 3]
Enter fullscreen mode Exit fullscreen mode

Detection

Since this is a "language feature", we can explicitly forbid it.

Tags

  • Mutability

  • JavaScript

Conclusion

We should always favour immutability on our designs and take extra care with side effects.

More Info

Credits

Photo by Zorik D on Unsplash

Thank you, @oliverjumpertz for this tip.


Correctness is clearly the prime quality. If a system does not do what it is supposed to do, then everything else about it matters little.

Bertrand Meyer


This article is part of the CodeSmell Series.

Top comments (0)

Need a better mental model for async/await?

Check out this classic DEV post on the subject.

β­οΈπŸŽ€ JavaScript Visualized: Promises & Async/Await

async await