Code Smell 86 - Mutable Const Arrays

Code Smell 86 - Mutable Const Arrays

Maxi Contieri

Published on Aug 25, 2021

1 min read

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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 ?
const array = [1, 2];

const newArray = [...array,3 ]

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

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, Oliver Jumpertz 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.

 
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