Chapter 19.5: node.js

CS 80: Internet Programming

Instructor: Mark Edmonds

Overview

• Node (node.js) enables server-side JavaScript
• Not a programming language, but rather a server-side application that allows you to program server-side applications in JavaScript
• Much of what we did with PHP can be done with node.js
• Node has much more functionality than PHP; you can basically write whatever JavaScript program you want without needing to execute in a browser

Overview

• Node is designed to make it easy to write I/O-based programs that run of a server
• I/O-based programs include web servers, databases, etc.

Overview

• Node uses event-based asynchronous processing
• We will use same event-listener and callbacks we learned in JavaScript

Installing Node

• Node can be installed from nodejs.org
• Node is a command-line program, and you start node with by typing node at your terminal/command prompt

Hello, world!

• Save the following in hello_world.js

              console.log("Hello, world!");

• Launch the program with

              node hello_world.js

Example: http_server.js

// basic HTTP server with an export
        var http = require("http"); // require the node HTTP module

        function onRequest(request, response)
        {
          console.log("Request received.");
          response.writeHead(200,
          {
            "Content-Type": "text/plain"
          }); // set HTTP response header
          response.write("Hello World"); // write content into HTTP request
          response.end(); // finishes the response
        }

        http.createServer(onRequest).listen(8888);

        console.log("Server has started.");
        

Modules

• We wrote var http = require("http"); in the HTTP server example
• http is a module that our node application requires
• But we also want to write our own models
• This is accomplished using exports

Example: http_server_export.js

// basic HTTP server with an export
        var http = require("http"); // require the node HTTP module

        function start()
        {
          function onRequest(request, response)
          {
            console.log("Request received.");
            response.writeHead(200,
            {
              "Content-Type": "text/plain"
            }); // set HTTP response header
            response.write("Hello World"); // write content into HTTP request
            response.end(); // finishes the response
          }

          http.createServer(onRequest).listen(8888);
          console.log("Server has started.");
        }

        exports.start = start;
        

Example: index.js

var server = require("./http_server_export");

        server.start();
        

Modules

• Modules are a core component of node.js
• They allow you to modularize code
• This breaks our I/O-based application easier to manage and scalable
• Each module can be responsible for a specific kind of I/O

Routing

• So far, every HTTP resquest was handled the same way
• Routing allows us to specify which modules process certain HTTP requests
• We'll look at the URL and the data in the GET/POST parameters and make a decision about where this HTTP request should be routed.

Example: router.js

        // create a router; this could also route to different applications (controllers) based on the file extension, or other information
        // here, we just print the request we are routing
        function route(pathname)
        {
          console.log("About to route a request for " + pathname);
        }

        exports.route = route;
        

Example: http_server_router.js

        var http = require("http"); // require the node HTTP module
        var url = require("url");

        function start(route)
        {
          function onRequest(request, response)
          {
            var pathname = url.parse(request.url).pathname;
            console.log("Request for " + pathname + " received.");

            route(pathname);

            response.writeHead(200,
            {
              "Content-Type": "text/plain"
            }); // set HTTP response header
            response.write("Request for " + pathname + " received."); // write content into HTTP request
            response.end(); // finishes the response
          }

          http.createServer(onRequest).listen(8888);
          console.log("Server has started.");
        }

        exports.start = start
        

Example: index_router.js

var server = require("./http_server_router");
        var router = require("./router");

        server.start(router.route);
        

Fileserver

• But we actually want our webserver to do something.
• Let’s write a basic webserver, capable of serving files to the client (similar to our Python SimpleHTTPServer we used earlier)

Example: http_fileserver.js

var http = require('http');
        var url = require('url');
        var fs = require('fs');

        function start(route)
        {
          function onRequest(request, response)
          {
            // look for file in current directory
            var filename = "." + url.parse(request.url).pathname;
            console.log("Request for " + filename + " received.");
            fs.readFile(filename, function(err, data)
            {
              // error getting the file, return a 404
              if (err)
              {
                response.writeHead(404,
                {
                  'Content-Type': 'text/html'
                });
                return response.end("404 Not Found");
              }
              // successfully retrieved file
              response.writeHead(200,
              {
                'Content-Type': 'text/html'
              });
              // write the file's data into the response
              response.write(data);
              return response.end();
            });
          }
          http.createServer(onRequest).listen(8888);
          console.log("Server has started.");
        }

        exports.start = start
        

Example: index_fileserver.js

var server = require("./http_fileserver");
        var router = require("./router");

        server.start(router.route);