JSFiddle - React, Tailwind, and code Playground

JavaScript

function Circle(r){
       var c = this;
       this.radius = r;
       this.getArea = function(){
         return this.radius * this.radius;
       }
    }
    
    var circle = new Circle(10);
     var d = circle.getArea;
        d(5);
    document.write(circle.getArea()+"<br/>");
    
    circle.radius = 20;
    
    document.write(circle.getArea()+"<br/>");
    
    var otherCircle = new Circle(1);
    document.write(otherCircle.getArea()+"<br/>");