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

function listener() {
  console.log('Previous:', prev ? prev.value : null);
  prev = this;
  console.log('Current:', this.value);
}
var prev, rad = document.forms.myForm.elements.myRadios;
for(var i = 0; i < rad.length; i++) {
  rad[i].addEventListener('click', listener);
}