function isEmpty(strfield1, strfield2, strfield3) {


//change "field1, field2 and field3" to your field names
strfield1 = document.forms[0].name.value 
strfield2 = document.forms[0].email.value
strfield3 = document.forms[0].phoneNumber.value

  //name field
    if (strfield1 == "" || strfield1 == null || !isNaN(strfield1) || strfield1.charAt(0) == ' ')
    {
    alert("\"Name\" is a mandatory field.\nPlease amend and retry.")
    return false;
    }

  //url field 
    if (strfield2 == "" || strfield2 == null || strfield2.charAt(0) == ' ')
    {
    alert("\"Email\" is a mandatory field.\nPlease amend and retry.")
    return false;
    }

  //title field 
    if (strfield3 == "" || strfield3 == null || strfield3.charAt(0) == ' ')
    {
    alert("\"Phone Number\" is a mandatory field.\nPlease amend and retry.")
    return false;
    }
    return true;
}