JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
<body>

<button id="button">Send Request</button>

<p id="demo"></p>


</body>
</html>

JavaScript

document.getElementById("button").addEventListener("click", function(e) {
  let first = 10;
  let second = 20;
  fetch('http://127.0.0.1/add?a=' + first + '&b=' + second)
    .then((response) => {
      return response.json();
    })
    .then((myJson) => {
      document.getElementById("demo").innerHTML = "When I add " + first + " and " + second + " I get: " + myJson.result;
    }).catch((error) => {
    	let fakeJSON = {
        result: first + second
      } // Only added to simulate
      document.getElementById("demo").innerHTML = "When I add " + first + " and " + second + " I get: " + fakeJSON.result;
    });
});