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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 ?

Right

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 favor immutability on our designs and take extra care with side effects.

Relations

Code Smell 116 - Variables Declared With 'var'

Code Smell 127 - Mutable Constants

More Info

The Evil Power of Mutants

Credits

Photo by Zorik D on Unsplash

Twitter

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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

Software Engineering Great Quotes

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This article is part of the CodeSmell Series.

How to Find the Stinky Parts of your Code