JSFiddle - React, Tailwind, and code Playground

HTML

<form name="myForm">
  <input type="radio" name="myRadios" value="1" />
  <input type="radio" name="myRadios" value="2" />
</form>

JavaScript

var prev;
document.forms.myForm.addEventListener('change', function(e) {
  if(e.target.name === 'myRadios') {
    console.log('Previous:', prev ? prev.value : null);
    prev = e.target;
    console.log('Current:', e.target.value);
  }
});