Creating an Express Project, Defining Routes, and Using next() for Control Transfer

Scenario

npm provides many third‑party modules, including many web frameworks. Express is chosen because it is stable, widely used, and the only web framework officially recommended by Node.js.

Implementation

Install Express

Install Express and the express‑generator tool globally:

npm install -g express
npm install -g express-generator

Run express --help to view usage.

Create a new Express project

Generate a project named microblog with the EJS template engine: express -t ejs microblog Enter the directory and install dependencies:

cd microblog
npm install

Add a listening port in app.js:

app.listen(3000,function () {
  console.log('服务端启动在3000端口')
})

Start the server with node app.js and open http://localhost:3000.

Add custom routes

Declare a new router for path /badao in app.js:

app.use('/badao', badaoRouter);
var badaoRouter = require('./routes/badao');

Create routes/badao.js:

var express = require('express');
var router = express.Router();

router.get('/', function(req, res, next) {
  res.send('这是来自badao--公众号:霸道的程序猿');
});

module.exports = router;

After restarting, http://localhost:3000/badao returns the response.

Route parameter matching

In routes/index.js add a parameterized route:

router.get('/hello/:username',function (req,res) {
  res.send('Hello:'+req.params.username);
});

Visiting http://localhost:3000/hello/YourName displays a personalized greeting.

Control transfer with next()

Express matches routes in definition order; later routes are ignored if an earlier one handles the request. Use the third next argument to pass control:

router.all('/:username',function (req,res,next) {
  if(users[req.params.username]) {
    next();
  } else {
    next(new Error(req.params.username+'不存在'));
  }
});
router.get('/:username',function (req,res) {
  res.send(JSON.stringify(users[req.params.username]));
});

This pattern validates the username parameter before returning the user object, demonstrating middleware and control transfer.

Example code download

Full source code is available at https://download.csdn.net/download/BADAO_LIUMANG_QIZHI/12969105