title: How to add folders in dat.gui?
body: <p>I'm trying to add folders for a the lights in a three.js project that i copied from a three.js example. But i can't get it working. I guess i should use f1=add.folder('light1') and then somehow add the parameters to f1 with f1.add('intensity') etc... but how to do this, when the code is structured like this ? node = f1.add() doesen't work!</p>
  
  <pre><code>        function buildGui() {
              clearGui();         
   /****************************** Light1 **************************/ 
              var f1 = gui.addFolder('Light1');
              addGui( 'lightcolor', spotLight.color.getHex(), function( val ) {
                  spotLight.color.setHex( val );
                  render();
              }, true );
  
              addGui( 'intensity', spotLight.intensity, function( val ) {
                  spotLight.intensity = val;
                  render();
              }, false, 0, 2 );
  
   /************************** Light2 **************************/  
              var f2 = gui.addFolder('Light2');
              addGui( 'lightcolor 2', spotLight2.color.getHex(), function( val ) {
                  spotLight2.color.setHex( val );
                  render();
              }, true );
  
              addGui( 'intensity 2', spotLight2.intensity, function( val ) {
                  spotLight2.intensity = val;
                  render();
              }, false, 0, 2 );
          }
  
          function addGui( name, value, callback, isColor, min, max ) {
              var node;
              param[ name ] = value;
  
              if ( isColor ) {
                      node = gui.addColor( param, name ).onChange( function() {
                      callback( param[ name ] );
                  } );
              } else if ( typeof value == 'object' ) {
                      node = gui.add( param, name, value ).onChange( function() {
                      callback( param[ name ] );
                  } );
              } else {
                      node = gui.add( param, name, min, max ).onChange( function() {
                      callback( param[ name ] );
                  } );
              }
              gui.remember(param);
              return node;
          }  
  </code></pre>