How to use powerful function composition in Javascript

Function composition is one of the most powerful differentiators between object-oriented and functional approaches to programming in JavaScript.

I will explain the difference between class hierarchy and composed function leading to practical examples of advantages of function composition and functional programming in JavaScript that I use in all of my own code.

Class hierarchy and RoboDog

In object-oriented programming, you define your classes.

For example, you specify a parent class Animal that has a method move. You continue by creating classes Cat and Dog which will inherit move from Animal and add their own methods bark and meow.

Then you decide to develop a class Robot which has a method chargeBattery.

Now, what if you want to create a class RoboDog that needs to move, chargeBattery and also, do a roboBark that enhances bark of your Dog? You need to inherit from both Dog and Robot but JavaScript does not allow you to do that.

To solve these and other issues, it is no longer recommended in object-oriented…