Form Validation Source Code (Annotated Version)

/****** Simple Validation Checking ******/

//---------------------------------------------------------------
// The ValidateInput function is called when the user
// clicks the Submit button. Before the values are
// submitted, this function makes sure that
// entries have been made in all boxes except Address2.
//---------------------------------------------------------------

function ValidateInput(form) {
     var LB = "\n"; // LB represents a Line Break
     var msgHdr = "Please fill out your:" + LB + LB; // Alert Header Message
     // The message the User will see informing her or him of any empty fields that are required
     var msg = "";

     // We are simply checking to see if the field is empty or not
     // if the field is empty then add the Field Information to the msg variable
     // NOTE: we could have also used -- if (form.First.value.length == 0)
     if (form.First.value == "") msg += "First Name" + LB;
     if (form.Last.value == "") msg += "Last Name" + LB;
     if (form.Address1.value == "") msg += "Address" + LB;
     // Note: Address2 is not mandatory

if (form.City.value == "") msg += "City" + LB;
if (form.State.value == "") msg += "State or Province" + LB;

     // NOTE: You can customize the following line for postal codes in your country
     // this is where you would call another function to take of this particular situation
     if (form.Postal.value == "") msg += "Postal Code" + LB;

// Verify that Age is a numeric w/ a value greater than 0 by converting it to an integer:
if (form.Age.value == "" || parseInt(form.Age.value) == 0) msg += "Age" + LB;

     // Make sure that the user makes a selection from the Income drop-down list:
     // the first selection is empty, so the user has to select something other than the first selection
     if (form.Income.options[form.Income.selectedIndex].value == "0") msg += "Income" + LB;

     // Make sure that a Female or Male radio button has been selected:
     // NOTE: The if statements says if male and the female radio buttons are not checked
     // then add that information to the msg variable
     // OR form.elements[9].checked == false && form.elements[10].checked == false
     if (form[9].checked == false && form[10].checked == false) msg += "Sex" + LB;

     // Display an alert if any of the input is missing:
     // the msg variable will only be empty if all the fields are filled out,
     // if not, the msg variable will contain the fields that are empty
     if (msg.length > 0){ // if the msg string is not empty, meaning some fields were left empty
          alert(msgHdr + msg);
         // return the document and the results back to the User
          // instead of "Submitting" the Form's Information to the server
          return false;
     }
     // "Submit" the Form's Information to the server for CGI processing.
     else return true;
}

/****** End of Validation Checking ******/

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Form "Validation"