function getRefToDiv(divID) {
        return document.getElementById(divID);
}

function showDiv(divID_as_a_string) {
    //get a reference as above ...
    myReference = getRefToDiv(divID_as_a_string);
    if ( myReference.style.display == 'block' ) {
        myReference.style.display = 'none';
    } else {
        myReference.style.display = 'block';
    }
}