one checkbox is checked.js

/** oneCheckboxIsCheckedInForm( form, message, matchName )
 * Returns true if at least one checkbox in the form is checked
 * Will show an alert message otherwise
 * Use in an onsubmit handler thus: 
 *    return oneCheckboxIsCheckedInForm(this)
 */
function oneCheckboxIsCheckedInForm( form, message, matchName ) {
    if ( !message ) {
        message = "You must check at least one checkbox before printing";
    }
    if ( !matchName ) {
        matchName = ".";
    }
    // loop through all the elements in the form
    for (var i = 0; i < form.elements.length; i++) {
        // If the element is a checkbox
        if (form.elements[i].type == "checkbox" && form.elements[i].name.match( matchName ) ) {
            // If the checkbox is checked
            if (form.elements[i].checked) {
                return true;
            }
        }
    }
    // else
    alert(message);
    return false;
}