Show/hide fields dynamically on Marketo forms.

gistfile1.html

<script type="text/javascript">
var $jQ = jQuery.noConflict();
$jQ(document).ready(function(){

//This code shows a field with ID = "State" when the value of field ID = "Country" is "Australia".
//Add this code to an HTML block on the landing page.

   // Put the ID of the dynamic field here
  var stateRow = $jQ("#State").parents("li:first");
  var stateField = $jQ("#State");

   // The ID of the controlling/triggering field
  $jQ("#Country").change(function() {
    var value = this.value;

     // when case value ="[Desired Value]", show the dynamic field and make it required
     // if not, hide the dynamic field
    switch(value)
    {
      case "Australia":
         stateField.addClass("mktFReq");
         stateRow.addClass("mktFormReq").slideDown();
         break;

      default:
         stateRow.removeClass("mktFormReq").slideUp();
         stateField.removeClass("mktFReq");
    }
  }).change();
  
});
</script>