June 2021
Intermediate to advanced
290 pages
9h 21m
Chinese
Content preview from Node与Express开发（第2版）
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调试
｜
239
static 中间件（node_modules/serve-static/index.js，
function staticMiddleware
）
一般来说，如果静态文件未按期望提供，问题则是出在你的路由，而不是这个
static
中
间件，因为路由优先于
static
中间件
。如果你有一个文件
public/test.jpg
以及一个路由
/test.jpg
，那么由于这个路由的存在
，
static
中间件将永远都不会得到调用。不过，如果
需要设置不同于静态文件的响应头，那么深入
static
中间件的源代码应该会有所帮助。
如果你绞尽脑汁想知道所有中间件都在哪里，那是因为
Express
本身带的中间件很少
（
static
中间件和路由是特别的例外）
。
就跟你在努力解决一个难题时深入
Express
的源代码会有所帮助一样
，你可能也不得不深
入中间件的源代码里面。这些中间件确实多到看不过来，但有
3
个我
想提一下，因为对于
理解在一个
Express
应用中会发生什么它们十分关键。
session 中间件（
node_modules/express-session/index.js，
function session
）
要让
session
正常工作
，涉及的东西很多，但是它的代码相当直白。如果遇到跟
session
有关的问题，就可以在这个函数里设置断点。要记住，为
session
中间件提供存储引擎
由你决定。
logger 中间件（
node_modules/morgan/index.js，
function logger
）
logger ...
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