JSFiddle - React, Tailwind, and code Playground

HTML

<strong>Output</strong>
<div id="output">

</div>

<hr />

<strong>Expected output</strong>
<div>
My dog Spot says: woof<br />
My cat Mittens says: meow<br />
My worm Squiggles says:  nothing
</div>

JavaScript

try {
  // create animal class
  var animal =  function(name) {
    this.name = name;
  };

  animal.prototype.getSound = function() {
    return this.sound === undefined ?  'nothing' : this.sound;
  };


  // create animal type classes
  var dog = new animal("dog");
  dog.prototype.sound = "woof";

  var cat = new animal("cat");
  dog.prototype.sound = "meow";

  var worm = new animal("worm");


  // create specific animals
  var spot = new dog();
  var mittens = new cat();
  var squiggles = new worm();
  
  // echo output
  document.getElementById("output").innerHTML = "My dog Spot says: " + spot.getSound() + "<br />"
    "My cat Mittens says: " + mittens.getSound() + "<br />"
    "My worm Squiggles says:  " + squiggles.getSound();
}
catch(e)
{
document.getElementById("output").innerHTML = e;
}