JSFiddle - React, Tailwind, and code Playground

HTML

<input type="radio" id="chlVal" name="selVal" value="Val 1"/>Value 1<br/>
<input type="radio" id="chkOther" name="selVal" value="Other"/>Other<br/>
<input type="text" id="txtOther">
    <button id="btn" onclick="Javascript: checkOther()" value='Check'>Check Form</button>

JavaScript

function checkOther()
{
    if (document.getElementById('txtOther').value!='')
    {
        alert('Value in the box');
        document.getElementById('chkOther').checked=1;
    }
}