How to prevent saving in global variable to know the last clicked radio button?

Question

I am trying to implement a grid with radio button selector. When the radio button is clicked, the row is set to a different color. Also, when a radio is selected in the grid, it needs to see if there was a previously selected radio button so that it could change the color set.

<script type="text/javascript">
var lastSelectedId = '';
function rowSelected(rdoButton) {

  if (rdoButton.id != lastSelectedId) {
    rdoButton.parentNode.parentNode.origClassName = 
      rdoButton.parentNode.parentNode.className;
    rdoButton.parentNode.parentNode.className = 'rowSelected';

    if (lastSelectedId != '') {
      var lastRadioButton = document.getElementById(lastSelectedId);
      lastRadioButton.parentNode.parentNode.className = 
        lastRadioButton.parentNode.parentNode.origClassName;
    }
  }
  lastSelectedId = rdoButton.id;
}
</script>

<table>
  <tr class="rowOdd">
    <td>
      <input type="radio" name="rdoGrpName" id="rdoId1" onclick="rowSelected(this);" />
    </td>
    <td>Blah</td>
  </tr>
  <tr class="rowEven">
    <td>
      <input type="radio" name="rdoGrpName" id="rdoId1" onclick="rowSelected(this);" />
    </td>
    <td>Blah</td>
  </tr>
</table>

I was wondering how I could remove the dependency on a global variable lastSelectedId to be able to track if there is a selected item? My initial idea is to save it to a dummy variable in the body object. like use this.

function rowSelected(rdoButton) {
  var mainBody = document.getElementByNames('body');
  if (rdoButton.id != mainBody[0].lastSelectedId) {
    // ....
  }
}

I was wondering if this is the right strategy for this. Also to make the code really unobstrusive, I need to add the event handler for the onload to initialize the global variable.

Answer 1

Couldn't you just check the class name of the td tag and see if it's the selectRow class and then change it if it is?

Answer 2

Perfectly would it be, when you assigned event-handlers inside the script not by using onclick attributes. Then you could store everything in a separate scope.

Now, you can also store the variable in a separete scope, but still the rowSelected/selectRow function has to stay in the global scope.

BTW. instead of saving the ID you can store the reference to the node itself.

var selectRow = (function(){
   var lastSelected, lastClass;

   return function(rdoButton){
      var p;
      if (rdoButton != lastSelected) {
         if (lastSelected) {
           p = lastSelected.parentNode.parentNode;
           p.className = lastClass;
         }
         p = rdoButton.parentNode.parentNode;
         lastClass = p.className;
         p.className = 'rowSelected';
      }
      lastSelected = rdoButton;
   }
})();