code: function getMap(id){
              var route = getRoute(id);
              var cache = jsonCache[route];
              if(!cache){
                  var filePath = path.join(root, route, 'map.json');
                  try{
                      cache = jsonCache[route] = JSON.parse(fs.readFileSync(filePath));
                  }catch(e){
                      throw e;
                  }
              }
              return cache;
          }
docs: 获取id所在json文件的json数据(如果在缓存中找不到对应数据,则读取文件)