JSFiddle - React, Tailwind, and code Playground

HTML

<form id="mainForm" name="mainForm">
    <input type="radio" name="rads" value="1" />
    <input type="radio" name="rads" value="2" />
    <input type="radio" name="rads" value="3" />
    <input type="radio" name="rads" value="4" />
</form>
<span id="result"></span>
<input type="text" name="erg" id="result" />

JavaScript

document.mainForm.onclick = function(){
    var radVal = document.mainForm.rads.value;
    result.innerHTML = 'You selected: '+radVal;
}