JSFiddle - React, Tailwind, and code Playground

HTML

<form name="form1" action="#" onsubmit="return validateForm()" method="post"> 
    First time visitor?:<br/>
            <label for="s1">Yes</label>
            <input type="radio" id="radio1" name="yesno" value="1"/>
            <br/>
            <label for="s2">No</label>
            <input type="radio" id="radio2" name="yesno" value="2"/>

            <br/>       

    <input type="submit" value="Submit"><br/>
    </form>

JavaScript

function validateForm() {
    var radios = document.getElementsByName("yesno");
    var formValid = false;

    var i = 0;
    while (!formValid && i < radios.length) {
        if (radios[i].checked) formValid = true;
        i++;        
    }

    if (!formValid) alert("Must check some option!");
    return formValid;
}