title: Passing control as parameter to javascript function
body: <p>I am trying to pass a control's id to a javascript function that adds the value of it(the control which is a textbox) to a listbox but apparently I am not getting it right, can someone please correct me. </p>
  
  <p>Thanks.</p>
  
  <pre><code>&lt;input type="button" ID="btnAddtoLstBox" value="" title="Add this to the list" onclick="javascript:addToList(document.getElementById(btnAddtoLstBox));"
  class="ui-icon ui-icon-refresh ui-corner-all" style="width: 20px; height: 20px; background-position: -64px 80px"  /&gt;
  
    // scripts to add list items
          function addToList(varTxtBox) {
  
                   // get the list box
                  var lb = document.getElementById("uilstMemTypeTier");
  
                  // get the text to add
                  var toAdd = varTxtBox.value;
  
                  if (toAdd == "") return false;
  
                  // look for the delimiter string. if found, alert and do nothing
                  if (toAdd.indexOf(delim) != -1) {
                      alert("The value to add to the list cannot contain the text \"" + delim + "\" as it is used as the delimiter string.");
                      return false;
                  }
  
                  // check if the value is already in the list box
                  for (i = 0; i &lt; lb.length; i++) {
                      if (toAdd == lb.options[i].value) {
                          alert("The text you tried to add is already in the list box.");
                          return false;
                      }
                  }
  
                  // add it to the hidden field
                  document.getElementById("&lt;%=uihdnlistBasedFieldsListItems.ClientID%&gt;").value += toAdd + delim;
  
                  // create an option and add it to the end of the listbox
                  lb.options[lb.length] = new Option(toAdd, toAdd);
  
                  // clear the textfield and focus it
                  varTxtBox.value = "";
                  varTxtBox.focus();
              }
  </code></pre>