# 应用程序分层,保持Express在其边界内

### 将组件代码分成web, services, DAL层 ![alt text](../../assets/images/structurebycomponents.PNG "Separate component code into layers")

### 1分钟说明:混合层的缺点 ![alt text](../../assets/images/keepexpressinweb.gif "The downside of mixing layers")