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

Be Explicit
Don't mix Booleans with non-booleans.
Fail Fast
Be Smarter than your compiler.
Stay loyal to the bijection.

The One and Only Software Design Principle

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

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 object 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