classesQuickly.md

Classes Quickly

Classes are part of object oriented programming. They're a little tricky to learn.

The aim of this is just to allow you to use them in a basic way.

A basic class

class Apple {

}

You can then talk about Apple by saying: Apple. It's as if const has been defined.

Adding a function (method)

Functions inside classes are called methods.

class Apple {

   color() {  // <- Just a normal function
     return 'red' 
   }

}

this

When you're inside a class there is a special invisible variable that's always there. It's called this.

this is only a thing inside a class. You can't use it outside a class.

Calling a method from a method

You do it using this.methodName()

class Apple {

   color() {  // <- Just a normal function
     return 'red' 
   }

   printColor() {
     console.log(this.color())
   }

}

Special constructor method

The constructor method is special. It always gets called whenever you 'use' a class.

class Apple {

   constructor() {
     super() // <- Must be here. Must go first
     console.log('This code gets called before anything else in the class')
   }

}

Where does the code go?

In methods. Nowhere else.

class Apple {
  console.log('THIS IS AN ERROR') // <- NOT ALLOWED

  color(shade) {
    console.log(shade) // <- This is fine
  }

}