var controllableObject = 
   {   
      numberProperty: 20,
      constrainedNum: 0,
      textProperty: "a string",
      booleanProperty: false,
      functionProperty: function() {
         alert("I am a function!");
      }
   };

window.onload = function() {

   GUI.start();
   
   // Creates a number box
   GUI.add(controllableObject, "numberProperty");
   
   // Creates a slider (min, max)
   GUI.add(controllableObject, "constrainedNum", -100, 100)
      .name("customName");
   
   // Creates a text field
   GUI.add(controllableObject, "textProperty");
   
   // Creates a checkbox
   GUI.add(controllableObject, "booleanProperty");
   
   // Creates a button
   GUI.add(controllableObject, "functionProperty");

};