ConstructorPattern.js

// Constructors

// Be careful when using 
// Constructor pattern
function C() { 
  this.instanceMember = 'Whoops!!' 
}

const c = C() // Forgot 'new'

c // <· undefined
window.instanceMember // <· 'Whoops!!'

// Always check if this is an 
// instance of the contructor
function C() { 
  if(!(this instanceof C))
    return new C()
  
    this.instanceMember = 'This is fine' 
}

const c = C() // Is this a constructor?

c // <· { instanceMember: 'This is fine' }
window.instanceMember // <· undefined