title: Google app script - callback confusion
body: <p>I'm confused about the behavior of the following code sample.
  Why can't I access statusLabelU in the callback via the app object ?</p>
  
  <p>It is available in the argument </p>
  
  <p>BTW, what is the type of the argument variable e in the callback ?</p>
  
  <pre><code>function doGet() {
    var app = UiApp.createApplication();
  
    var button = app.createButton('Enter Symbol');
    app.add(button);
  
    var symbolText = app.createTextBox().setName('symbolText').setId('symbolText');
    app.add(symbolText);
  
    var labelU = app.createLabel('Unknown symbol U')
                   .setId('statusLabelU');
  
    var labelK = app.createLabel('Unknown symbol K')
                   .setId('statusLabelK');
    app.add(labelU);
    app.add(labelK);
  
    var handler = app.createServerHandler('myClickHandler');
  
    handler.addCallbackElement(symbolText);
    button.addClickHandler(handler);
  
    return app;
  }
  
  function myClickHandler(e) {
    var app = UiApp.getActiveApplication();
  
    var symU = app.getElementById('symbolText');
    var symK = e.parameter.symbolText;
  
    var financeU = FinanceApp.getStockInfo(symU);
    var financeK = FinanceApp.getStockInfo(symK);
  
    var label = app.getElementById('statusLabelU');
    label.setText(financeU.name);
  
    var label = app.getElementById('statusLabelK');
    label.setText(financeK.name);
  
    app.close();
    return app;
  }
  </code></pre>