ExpressJs Study Note

This is a study note of the first two parts of the book Express in Action.

1. Introduction

Express is a routing + sugar layer on top of Node.js HTTP server that simplifies Node APIs. It introduces a plugin framework and adds new functions such as routing and rendering.

A middleware is a small request handler function in Express. It has full access to the request and response parameters. These functions are chained in a pipeline.

Routing examines request method and URL to call different request handleer functions.

Express allows you to break a large application into small subapplicaitons called routers.

The let app = express() creates a request handler object and assigns it to app. The app is both a function and an object that has many methods for.

  • routing requests: app.METHOD and app.param. The METHOD can be get, put, post and so on.
  • configuring middleware: app.route
  • rendering HTML views: app.render
  • registering a template engine: app.engine

2. Middleware

In Node HTTP server, all requests are handled by a request handler funciton that takes a request and a response parameters. Express let you use an array of functions chained together instead of a big one. app.use(function(req, res, next)) installs a middleware.

There are many third-party Express middlewares such as logger (Morgan), body parser, cookie parser, security and so on.

3. Routing

You can use path in app.METHOD in a syntax like hello/:who format. who can be accessed as request.params.who.

Using app.use('my-path', my-router) to setup routers. Each router is like a mini-application that can handle request for a specific path.

4. Extending request and response

Express add methods such as request.ip, response.redirect(), response.sendFile() , response.send() and so on to the response parameter.


Express can set views path and view engine.

Written on January 2, 2017