JSFiddle - React, Tailwind, and code Playground

HTML

<label for="gender">Gender: </label>
<input type="radio" name="genderS" value="1" checked="checked">Male</input>
<input type="radio" name="genderS" value="0" >Female</input>

JavaScript

var radios = document.getElementsByName('genderS');

for (var i = 0, length = radios.length; i < length; i++) {
    if (radios[i].checked) {
        // do whatever you want with the checked radio
        alert(radios[i].value);

        // only one radio can be logically checked, don't check the rest
        break;
    }
}