Infinite code, smells! It smells because there are likely many instances where it could be edited or improved. Most of these smells are just hints of something that might be wrong. They are not required fixed per se… ( You should look into it though.) Previous Code Smells Part I Part II Part III Part IV Part V Part VI Part VII Part VIII Part IX Part X Part XI Part XII Part XIII Part XIV Part XV Part XVI Part XVII Let's continue... 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 Use better languages 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 favour immutability on our designs and take extra care with side effects. More Info The evil power of mutants Credits Photo by on Zorik D Unsplash Twitter 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 Code Smell 87 - Inconsistent Parameters Sorting Be consistent with the parameters you use. Code is prose. TL;DR: Don't confuse you readers. Keep the order. Problems Readability Consistency Solutions Refactor and change parameters order. Use named parameters Sample Code Wrong function giveFirstDoseOfVaccine(person, vaccine) {
  //
}

function giveSecondDoseOfVaccine(vaccine, person) {
  //
}


giveFirstDoseOfVaccine(jane, pfizer);
giveSecondDoseOfVaccine(jane, pfizer);  //Unnoticed mistake Right function giveFirstDoseOfVaccine(person, vaccine) {
  //
}

function giveSecondDoseOfVaccine(person, vaccine) {
  //
}


giveFirstDoseOfVaccine(jane, pfizer);
giveSecondDoseOfVaccine(jane, pfizer);  //Jane is immunized Detection Some very smart linters may be able to compare arguments and hint for possible mistakes. Tags Readability Conclusion This is a very simple smell. Readability is very important to avoid mistakes. Relations Code Smell 10 - Too Many Arguments Credits Photo by on Lance Grandahl Unsplash Twitter Computers are good at following instructions, but not at reading your mind. Donald Knuth Code Smell 88 - Lazy Initialization Yet another premature optimization pattern TL;DR: Do not use lazy initialization. Use an object provider instead. Problems Surprising Side Effects Premature Optimization Fail Fast Violation Implementative Coupling The Least Surprise Principle Violation Null Usage Mutability Transactional and Multi-threaded applications problems Debugging Problems Solutions Inject Responsibilities with First Class Objects Sample Code Wrong class Employee
  def emails
    @emails ||= []
  end
  
  def voice_mails
    @voice_mails ||= []
  end
end Right class Employee
  attr_reader :emails, :voice_mails

  def initialize
    @emails = []
    @voice_mails = []
  end
end
#We can also inject a design pattern to externally deal
#with voice_mails so we can mock it in our tests Detection Lazy initialization is a common pattern when used checking for a non-initialized variable. It should be straightforward to detect them. Tags Premature Optimization Conclusion are another antipattern often combined with lazy initialization. Singletons We must avoid premature optimizations. If we have performance problems we should use a Proxy, Facade or more independent solution. real Relations Code Smell 32 - Singletons Code Smell 12 - Null More Info Wikipedia Martin Fowler Credits Photo by on Sam Solomon Unsplash We have to stop optimizing for programmers and start optimizing for users. Jeff Atwood Code Smell 89 - Math Feature Envy One class calculating formulas for another class. TL;DR: Leave the formulas to the objects gathering the information. Problems Declaratively Low reuse Real-world concept missing Encapsulation Solutions Move the math formula to the class Search for real-world abstractions Sample Code Wrong function area(rectangle) { 
  return rectange.width * rectangle.height;
  //Notice we are sending consecutive messages to
  //the same object and doing calculations
} Right class Rectangle {
    constructor(width, height, color) { 
         this.height = height;
         this.width = width;
    }
 
    area() {
        return this.width * this.height;
    }
} Detection Since many cascading messages are sending to the same object, we can detect a pattern. Tags Encapsulation Coupling Conclusion This is a very basic smell. If we are manipulating another object characteristics, we should let it do it the maths for us. Relations Code Smell 63 - Feature Envy More Info The one and only one software principle Credits Photo by on Michal Matlon Unsplash Computer science is not about machines, in the same way that astronomy is not about telescopes. There is an essential unity of mathematics and computer science. Michael R. Fellows Code Smell 90 - Implementative Callback Events When creating events, we should decouple the trigger from the action. TL;DR: Name your functions acording to what happened. Problems violation Observer Pattern Coupling Solutions Name the events after "what happened", not "what you should do". Sample Code Wrong const Item = ({name, handlePageChange)} =>
  <li onClick={handlePageChange}>
    {name}
  </li>

//handlePageChange is coupled to what you decide to do
//instead of what really happened
//
//We cannot reuse this kind of callbacks Right const Item = ({name, onItemSelected)} =>
  <li onClick={onItemSelected}>
    {name}
  </li>

//onItemSelected will be called just when a item was selected. KISS
//Parent can decide what to do (or do nothing)
//We defer the decision Detection This is a semantic smell. We can detect it on peer code reviews. Tags Coupling Naming Conclusion Names are very important. We should delay implementation coupled names until the very last moment. More Info What is exactly in a name Refactoring Guru Credits Photo by on Ashim D’Silva Unsplash Thanks to Maciej for this tip Twitter Beyond basic mathematical aptitude, the difference between good programmers and great programmers is verbal ability. Marissa Mayer And that’s all for now… The next article will explain 5 more code smells!

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