How to update a table row with save button using .ajax

I have a table which has one row and only one cell will be editable. I have accomplished this with the following code.

$("td#effEndDate").click(function() {
            if (!$(this).hasClass("edit")) {
                var value = jQuery.trim($(this).html());
                $(this).html("<input id=\"txtEdit\" type=\"text\" value=\"" + value + "\" />");
                $(this).addClass("edit");
                $("#txtEdit").focus();
            }
        });

Now this is the part where i'm stuck.

After the field is updated a save button must be clicked to call the proper .ajax method to update the database. But how can I compare the previous value to the current value on a button press? Since i'm not using the onblur property where I could have saved the old value and passed it to the update function.

Solution

There are two possibilities.

Pass the variable around in between functions
Make the variable global

if you want the variable global do not use the "var" keyword

Change:

var value = jQuery.trim($(this).html());

To this:

value = jQuery.trim($(this).html());

Edit

If the click function is getting hit more then once before a page refresh and assuming you want to keep a copy of the original table rows you can try this. Save a copy of the original table in a variable then you can query the original table for the html using the ID number. Here is a quick mock

first store the table in a variable upon the page loading. This will save an original copy of the table

 //get a copy of the table
 var GetCopyofOriginalTable = function() {
      var TableToBeCopied = $('the appropriate selector');
      CopyOfTable = JQuery.extend(true, {}, TableToBeCopied);  //Notice no var, its global
 }

 //Now store the variale
 GetCopyofOriginalTable();

 var FindTableRowByID = function(trID) {
      return $('table:has(tr#' + trID));
 }

Now you can loop through the new table test its value agaisnt the old table. This methed make use alot of memory depending on how big the table is.