JavaScript で選択したラジオ ボタンの値を効率的に取得するにはどうすればよいですか?

function findSelection(field) {
    var test = 'document.theForm.' + field;
    var sizes = test;
    for (i=0; i < sizes.length; i++) {
        if (sizes[i].checked==true) {
            return sizes[i].value;
        }
    }
}

document.querySelector('input[name="genderS"]:checked').value;

<form action="#n" name="theForm">
    <label for="gender">Gender: </label>
    <input type="radio" name="genderS" value="1" checked> Male
    <input type="radio" name="genderS" value="0" > Female<br><br>
    <a href="javascript: submitForm()">Search</a>
</form>

function submitForm() {
    var gender = document.querySelector('input[name="genderS"]:checked').value;
    alert(gender);
}