JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://popcornjs.org/code/dist/popcorn-complete.min.js"></script>

JavaScript

var xhr = new XMLHttpRequest();;

var states = function() {
    
   if (xhr.readyState == 4 && xhr.status == 200) {
    alert(xhr.responseText);
  }
}

xhr.open('GET',
  'https://ap1.salesforce.com/services/apexrest/Account/0019000000RLvA6');
xhr.setRequestHeader('Authorization:',
  'Bearer ' + '00D90000000noBP!AQwAQPGVOJ_09qBN.l:YE2KiSbOMsAngDHz4m2pJcF0OEHt0X67AKGmN9yB5ejjl8745SmMHXJDtMFb0Kc.hJu16jsndMXnIa');
xhr.setRequestHeader("Content-Type","application/json");
xhr.send();
    
states();
alert(xhr.responseText);