Skip to content

Express

Jump to bottom
all1124 edited this page Oct 18, 2019 · 5 revisions

Express

Using Express Middleware

  • Express is a routing and middleware web framework
  • An Express application is essentially a series of middleware function calls
  • Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle
  • The next middleware function is commonly denoted by a variable named next
  • Middleware functions can perform the following tasks:
    • Execute any code
    • Make changes to the request and the response objects
    • End the request-response cycle
    • Call the next middleware function in the stack
  • Application-level middleware
    • app.use()
    • app.METHOD() functions
  • Router-level middleware
    • router.use()
    • router.METHOD() function
  • Error-handling middleware
    • You must provide four arguments to identify it as an error-handling middleware function

Express Middleware

  • These functions are used to modify req and res objects for tasks like parsing request bodies, adding response headers, etc `var express = require('express'); var app = express();

        //Simple request time logger
    app.use(function(req, res, next){
    console.log("A new request received at " + Date.now());

     //This function call is very important. It tells that more processing is
     //required for the current request and is in the next middleware
     function/route handler.
     next();
    });

    app.listen(3000);`

  • To restrict it to a specific route (and all its subroutes), provide that route as the first argument of app.use()

  • One of the most important things about middleware in Express is the order in which they are written/included in your file; the order in which they are executed, given that the route matches also needs to be considered

  • Third Party Middleware

    • body-parser

      • This is used to parse the body of requests which have payloads attached to them `var bodyParser = require('body-parser');

          //To parse URL encoded data
 app.use(bodyParser.urlencoded({ extended: false }))

 //To parse json data
 app.use(bodyParser.json())`
    • cookie-parser

      • It parses Cookie header and populate req.cookies with an object keyed by cookie names

          `var cookieParser = require('cookie-parser');
   app.use(cookieParser())`

Video

Additional Resources

Clone this wiki locally