JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://sinonjs.org/releases/sinon-1.7.3.js"></script>

JavaScript

showForm = function (url) {
         $.get(url, function (html) {
             $('body').append();              
        });
 }; 

var server = sinon.fakeServer.create();
server.respondWith('{}');
var spy = sinon.spy($.fn, "append");             
showForm('/fake');
server.respond();
console.log(spy.called)