An example of coupling and decoupling in Javascript

structure_coupling.js

//this type of coupling happens when you expose the internals object A to object B
//in this example we are accessing a method and assigning a property. 
//this type of coupling happens when one module asks a question of another module
//if Person changes how it represents 'hasHobby' it breaks the coupled version in
//2 places
//by using a 3rd object to hold that information we only break the code in 1
//place if we ever change how the Person represents hwo they have a hobby

//coupled
function main(){
  
  var hobby = 'rowing';
  var person1 = new Person();
  var person2 = new Person();
  
  //update the person1 hobby
  if(person1.needsHobby()){
    person1.hobby = hobby;
  }
  
  //update person2 hobby
  if(person2.needsHobby()){
    person2.hobby = hobby;
  }
  
}

//decoupled/ioc
function main(){
  
  var hobby = 'rowing';
  var person1 = new Person();
  var person2 = new Person();
  var hobbyUpdater = new HobbyUpdater();
  
  hobbyUpdater.update(person1,hobby);
  hobbyUpdater.update(person2,hobby);
  
}