Need JQuery Function to check if field is Null in ASP.NET (SharePoint)

I have a form that I am building in SharePoint Designer 2007 that has several fields that are required depending on the value of a specific field, so I need to create my own required field indicator. For example

when field is empty:
label     Field1 *

when field has a value:
label     Field1
 
I would like to have an '*' next to an empty required field and have the '*' be hidden when the field(s) has a value.

Another problem I am having is that when I use the <SharePoint:FormField ..../> tag with a <P>*</P>.   The '*' is put on another line instead of next to my field.
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Michael CarrilloInformation Systems ManagerAsked:
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Ted BouskillSenior Software DeveloperCommented:
There are client-side validation controls available in ASP.NET that will do what you require.  They generate the client side JavaScript & also validate the forms server-side to do things like prevent SQL injection attacks.  Why are you not using them?
Michael CarrilloInformation Systems ManagerAuthor Commented:
I need to build a form that has required fields that are dependent on the value of a field as follows:

Field 1 (Required)*
Field 2 (not Required)

Field 3 (If Field 1 = A then Required and visible else Not required and Hidden)*
Field 4 (if Field 1 = B Then Required and visible else Not required and Hidden)*

I want the '*' to appear next to required fields and disappear when the field has data.
so far I have a function that is not working ( I know I am using the click event instead of the change event to accelerate testing) as follows:

$(document).ready(function()    {
     $("input[id*=ff5]").click(function()    {
         $("div#ff5".hide();
         });
});

This is within a <Script type="text/javascript"> tag and of course include the Script with the jquery-1.7.2.js src.

I used the input tag because I can't directly reference SharePoint:FormField.

I do have a question; does it matter if I use the single quote or double quotes?
Michael CarrilloInformation Systems ManagerAuthor Commented:
Ah!  Turned out I misspelled the jquery src.  So now this works.
Now I need to make this an on change event and check if it is null.
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Ted BouskillSenior Software DeveloperCommented:
Michael CarrilloInformation Systems ManagerAuthor Commented:
Ok,

How do I adapt this function to check if the field is Null?

$(document).ready(function()    {
     $("input[id*=ff5]").Change(function()    {
         $("div#ff5".hide();
         });
     $("input[id*=ff5]").Change(function()    {
         $("div#ff5".show();
         });

});
Ted BouskillSenior Software DeveloperCommented:
There is no such thing as Null on the client.  You have to check for an empty string or a string length of 0

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Michael CarrilloInformation Systems ManagerAuthor Commented:
I was able to get this to work with your suggestions and some additional informaiton from StackOverflow.

$(document).ready(function()    {
     $("input[id*=ff5]").Change(function()    {
          var f=$.trim(S("input[id*=ff5]").val()).length;
          if(f==0) {
              $("div#ff5").show();
          }
          else   {
              $("div#ff5").hide();
         }
         });
});

Thanks Again!

I will most likely be opening another question on Monday to adapt this function to validate multiple
fields instead of just a single specific field.
Michael CarrilloInformation Systems ManagerAuthor Commented:
I select my comment as part of the solution as it was a summation of all the suggestions needed to complete the solution.
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