JSFiddle - React, Tailwind, and code Playground

HTML

<input type="radio" name="r" data-number="2" value="Radio 1">Radio 1
<input type="radio" name="r" data-number="4" value="Radio 2">Radio 2
<input type="radio" name="r" data-number="8" value="Radio 3">Radio 3

<div class="result">Result</div>

JavaScript

var radios = document.querySelectorAll('input[type=radio]');
var result = document.querySelector('.result');
var a;

for (var i = 0; i < radios.length; i++) {
    radios[i].addEventListener('change', function() {
        a = this.dataset.number;
    });
}
result.innerHTML = a;