title: date and time in textbox googlescripts
body: <p>Hello im new with Programming and with googlescripts i hope some can help me, i make as a test  app just a simple textbox with a button and i want to change the value of the textbox and show the date and the time  when i clicking on the button , i have trid to write this code but i dont know where is the wrong in it 
  thank you all</p>
  
  <pre><code> function doGet() {
        var app=UiApp.createApplication().setTitle('test app');
        var pan1=app.createHorizontalPanel();
        app.add(pan1);
        var txt1=app.createTextBox().setId(txt1);
        var btn1=app.createButton().setText('start').setId('btn1');
        btn1.addClickHandler(app.createServerHandler("now"));
        pan1.add(txt1);
        pan1.add(btn1);
        return app;
  }
  
  function now() {
       var app =UiApp.getActiveApplication();
       app.getElementById("txt1").setText(new Date());
       return app;
  }
  </code></pre>