Posted on Aug 25, 2021 • Edited on Aug 30, 2021 • 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

const array = [1, 2]; array.push(3) //array => [1, 2, 3] //Wasn't it constant ? //constant != immutable ?

const array = [1, 2]; const newArray = [...array,3 ] //array => [1, 2] Didn't mutate //newArray = [1, 2, 3]

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

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

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.