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Cover image for Code Smell 69 - Big Bang (JavaScript Ridiculous Castings)
Maxi Contieri
Maxi Contieri

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Code Smell 69 - Big Bang (JavaScript Ridiculous Castings)

This handy operator is a trouble maker.

TL;DR: Don't mix booleans with non-booleans.

Problems

  • Not Declarative Code

  • Hard to debug

  • Magic Castings

  • Accidental Complexity

Solutions

  1. Be Explicit

  2. Don't mix Booleans with non-booleans.

  3. Fail Fast

  4. Be Smarter than your compiler.

  5. Stay loyal to the bijection.

Sample Code

Wrong

!true // returns false
!false // returns true

isActive = true 
!isActive // returns false

age = 54
!age // returns false
array = []
!array // returns false
obj = new Object;
!obj // returns false

!!true // returns true
!!false // returns false

!!isActive // returns true
!!age // returns true
!!array // returns true
!!obj // returns true
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Right


!true // returns false
!false // returns true

isActive = true 
!isActive // returns false

age = 54
!age // should return type mismatch (or 54 factorial!)
array = []
!array // should return type mismatch
obj = new Object;
!obj // should return type mismatch (what is an obejct negated in a real domain?)

!!true // returns true - it is idempotent
!!false // returns false - it is idempotent

!!isActive // returns true - it is idempotent
!!age // nonsense
!!array // nonsense
!!obj // nonsense
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Detection

Since this is a "feature" in some languages it would be hard to test. We can set programming policies or choose more strict languages.

We should detect ! !! usages in non-boolean objects and warn our programmers.

Tags

  • Casting

  • Coercion

  • Javascript

Conclusion

Languages like JavaScript divide their whole universe into true or false values. This decision hides errors when dealing with non booleans.

We should be very strict and keep booleans (and their behavior), far away from non booleans.

Relations

More info

Reddit

Double Bang

Mozilla

Credits

Photo by Greg Rakozy on Unsplash


It is easier to write an incorrect program than understand a correct one.

Alan J Perlis


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