code: function (classes) {
              var extensions = this.props.extensions;
  
              if (extensions && extensions.get("addClass")) {
                  var data = this.getDataForExtension();
                  classes = classes + " " + extensions.get("addClass").map(function (callback) {
                      try {
                          return callback(data);
                      } catch (e) {
                          console.error("Exception thrown in FileTreeView addClass provider: " + e, e.stack);
                      }
                  }).filter(isDefined).toArray().join(" ");
              }
  
              return classes;
          }
docs: Calls the addClass providers to get the classes (in string form) to add for the current
  file or directory.
  
  @param {string} classes Initial classes for this node
  @return {string} classes for the current node