JSFiddle - React, Tailwind, and code Playground

JavaScript

// Using the prototype.
function Size(width, height) {
    this.width = width;
    this.height = height;
}

    Size.prototype.area = function() {
       return this.width * this.height;
    };

// Using instance methods and fields.
    function Size2(width, height) {
       this.width = width;
       this.height = height;
       this.area = function() {
          return this.width * this.height;
       }
    }

var s = new Size(5, 10);
var s2 = new Size2(5, 10);

print("Size");
print(s.area());

print("Size 2");
print(s2.area());

// Looks identical, but lets use the reference equality operator to test things:
var s3 = new Size2(5, 10);
var s4 = new Size(5, 10);

print(s2.area == s3.area); // oops, it's false
print(s.area === s4.area);



function print(x) {
    document.body.innerHTML += "<p>" + x + "</p>";
}