JSFiddle - React, Tailwind, and code Playground

HTML

<h1>if you see this before the alert everything is ok!</h1>

JavaScript

function loadpapi(){
    alert("Hello World!");
}


function pctaddLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}

pctaddLoadEvent(loadpapi);