JSFiddle - React, Tailwind, and code Playground

JavaScript

var t = prompt("Input your code.");
var d = ["A", "a", "U", "u", "X", "x", "+", "&", "#", "6", "5", "4", "1", "9", "7", "0"];

if(d.indexOf(t) > -1)
{
  alert("Contains a disallowed character!");
}

// Stack Exchange is love, Stack Exchange is life.

// http://stackoverflow.com/a/4444497/5513988
// Modified that if statement from above link

// http://stackoverflow.com/a/18588905/5513988
// Then changed to this