code: function(pathname) {
          var prefix = this._options.root + pathname;
          var paths;
          if (pathname.charAt(pathname.length - 1) === "/") {
              // pathname是个路径，比如： /path/name/
              paths = [   prefix + "index.js",
                  prefix + "index.json",
                  prefix + "index.html"
              ];
          } else {
              var result = ExtReg.exec(pathname);
              if (result && result[1]) {
                  // pathname有后缀，比如：/path/to/filename.do
  
                  var ext = result[1].toLowerCase();
                  if (ext != "js") {
                      paths = [   prefix + ".js",
                          prefix + ".json",
                          prefix + ".html"
                      ];
                  }
                  paths.push(prefix);
              } else {
                  // pathname没有后缀，比如：/path/name
                  paths = [   prefix + ".js",
                      prefix + ".json",
                      prefix + ".html",
                      prefix + "/index.js",
                      prefix + "/index.json",
                      prefix + "/index.html"
                  ];
              }
          }
  
          return paths;
      }
docs: 获得可能的路径名
  @param pathname
  @returns {Array}
  @private