Code Smell 18 — Static Functions

Yet another global access coupled with laziness.

TL;DR: Don't use static functions. They are global and utilities. Talk to objects instead.

Problems

Coupling
Testability
Protocol Overloading
Cohesion

Solutions

Class Single Responsibility Principle is to create instance. Honor it.
Delegate method to instance.
Create stateless objects. Don't call them helpers.

Examples

Static class methods
Static attributes

Sample Code

Wrong

class DateStringHelper {
   static format(date) {
     return date.toString('yyyy-MM-dd'); ;    
  }
}


DateStringHelper.format(new Date());

Right

class DateToStringFormatter {
   constructor(date){
      this.date = date;
   }

   englishFormat() {
     return this.date.toString('yyyy-MM-dd');    
  } 
}

new DateToStringFormatter(new Date()).englishFormat()

Detection

We can enforce a policy to avoid static methods (all class methods but constructors).

Conclusion

Class are globals disguised. Polluting their protocol with "library methods" breaks cohesion and generates coupling. We should extract static with refactorings.

In most languages we cannot manipulate classes and use them polymorphically, so we can't mock them or plug them on tests.

Therefore, we have a global reference too difficult too decouple.