How to use javascript function in jstl if condition

Question

This is my javascript function:

function isEmpty(field){
    if( document.getElementsByName(field).value === '' )
        return true;
    return false;
}

How to use my javascript function in jstl here:

<c:choose>
    <c:when test ="isEmpty(firstName)">
        <span class="red">please-fill-required-fields</span>
    </c:when>
    <c:otherwise>
        <span class="red"> </span>
    </c:otherwise>
</c:choose>

Answer 1

Jstl codes execute on server side and javascript functions execute after rendering the page by server! So, you can't use javascript inside jstl code. Instead, you should use jstl(not javascript) for checking null value.