Node.js Express route-specific vs top-level generic parsing

Question

What's the advantage of using top-level generic parsing:

// parse application/x-www-form-urlencoded
app.use(bodyParser.urlencoded({ extended: false }))

// parse application/json
app.use(bodyParser.json())

instead of route-specific parsing:

// create application/json parser
var jsonParser = bodyParser.json()

// create application/x-www-form-urlencoded parser
var urlencodedParser = bodyParser.urlencoded({ extended: false })

// POST /newUser gets urlencoded bodies
app.post('/newUser', urlencodedParser, function (req, res) {
  if (!req.body) {
      return res.sendStatus(400)
  } else {
  ...
  }
})

According to the body-parser readme it says the route-specific is the most recommended way. Why? Why use it instead of top-level generic parsing?

Answer 1

原因是无条件执行中间件意味着当请求已经不满足任何前提条件（例如匹配路由或满足身份验证要求）时，您可能正在执行不必要的工作。