Dr. Greg Bernstein
Updated September 15th, 2021
package.json, open source repository, script runnerA way of running JavaScript outside of a browser.
Node.js® is a JavaScript runtime built on Chrome’s V8 JavaScript engine.
Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.
Node.js’ package ecosystem, npm, is the largest ecosystem of open source libraries in the world.
Node.js is available for free from https://nodejs.org/en/download/.
Linux, Mac, and Windows operating systems are supported.
Note that you do not need the extra build tools! These take 3GB of space on windows.
For a console-like JavaScript shell type node in a windows, Mac, or Linux command window. Use .exit to exit.
To run a JavaScript file type node Filename.js from a command shell.
JavaScript operations in browsers are heavily restricted from touching the host computer, particularly the file system.
Via the Node.js API JavaScript programs have access to the file system, network, and some OS services.
For a console like JavaScript shell type node in a windows, Mac, or Linux command window. Use .exit to exit.
To run a JavaScript file type node Filename.js from a command shell.
File hiNode.js, run with node hiNode.js
// File: hiNode.js
let a = [1, 3, 5, 7, 9, 11];
function cube(x) {
return x*x*x;
}
console.log("Hello from Node.js");
for (let x of a) {
console.log(`x = ${x} and x cubed = ${cube(x)}`);
}Node.js now supports ES6 modules
import syntaxexport syntaxGetting a list of all files in a directory fileList.mjs
// List all the files in the current directory
// ES6 module syntax
import fs from 'fs'; // File system module
let allFiles = fs.readdirSync(".");
console.log("Files in the current directory: ");
allFiles.forEach(function(f) { console.log('\t' + f); });Simple File Reading syncRead.mjs
// Simple Synchronous file reading
// Using ES6 Modules.
import fs from 'fs'; // File system module
let fname = './whoAmI.js';
let fdata = fs.readFileSync(fname, 'utf8');
console.log("Contents of file whoAmI.js:");
console.log(fdata);File syncWrite.mjs
// Simple Synchronous file Write
// ES6 modules
import fs from 'fs'; // File system module
let fname = './tempWrite.txt';
let data = "Just a little text. \n Did this write?";
let fdata = fs.writeFileSync(fname, data);
console.log("Wrote test file: tempWrite.txt");Getting information about network interfaces netIf.mjs
// A simple program to look at IPv4 addresses
// for network interface via Node.js and ES6 modules
import os from 'os';
let networkInterfaces = os.networkInterfaces();
// console.log(networkInterfaces); // Shows everything
for (let intf in networkInterfaces) {
console.log(intf);
// Only interested in IPv4 interfaces
let addresses = networkInterfaces[intf]
.filter(a => a.family === 'IPv4');
console.log(addresses);
}Read and Parse JSON quickJSON.mjs
// JSON reading and parsing with Node.js ES6 modules
import { readFile } from 'fs/promises'; // promise based file reading
const clubEvents = JSON.parse(await readFile(new URL('./eventData.json',
import.meta.url))); // URL for relative file location, regular JSON parsing
clubEvents.forEach(function(event) { //Look at data
console.log(event);
});In the Globals section of the API documents you will find
_dirname, _filename CommonJS onlyrequire() CommonJS onlyconsole for simple output and debugging always availableWhen running a JavaScript file Node under CommonJS provides some global variables:
__filename the full file name of this JavaScript file__dirname the directory this file is inThe following program is from the file whoAmI.js and is run with node whoAmI.js.
console.log("Hello from Node.js");
console.log("The name of this file is: " + __filename);
console.log("This file is in the directory: " + __dirname);Node.js has a module system that predates the ES6 standard
const varName = require('moduleName');Getting a list of all files in a directory fileList.js
// List all the files in the current directory
const fs = require('fs'); // Import file system module
let allFiles = fs.readdirSync(__dirname);
console.log("Files in the current directory: " + __dirname);
allFiles.forEach(function(f){console.log('\t' + f);});Simple File Reading syncRead.js
// syncRead.js
const fs = require('fs'); // File system module
let fname = __dirname + '/whoAmI.js';
let fdata = fs.readFileSync(fname, 'utf8');
console.log("Contents of file whoAmI.js:");
console.log(fdata);File syncWrite.js
// syncWrite.js
const fs = require('fs'); // File system module
let fname = __dirname + '/tempWrite.txt';
let data = "Just a little text. \n Did this write?";
let fdata = fs.writeFileSync(fname, data);
console.log("Wrote test file: tempWrite.txt");Getting information about network interfaces netIf.js
// netIf.js
// Let's look at your machines IPv4 addresses
const os=require('os');
let networkInterfaces = os.networkInterfaces();
// console.log(networkInterfaces); // Shows everything
for (let intf in networkInterfaces){
console.log(intf);
// Only interested in IPv4 interfaces
let addresses = networkInterfaces[intf]
.filter(a => a.family === 'IPv4');
console.log(addresses);
}From npmjs.com
npm is the package manager for JavaScript and the world’s largest software registry.
It also offers a simple script running system.
All the development tools and JavaScript libraries we will be using will be obtained via npm. npm gets installed with Node.js. npm can take some time to install packages.
See npm docs
npm install <package_name> See local installSee npm docs
npm install -g <package_name> See global install
npm install -g http-serverhttp-serverserve --help to see options“A global install doesn’t work for me…”
Do a local install: npm install http-server
In the directory where you installed it, Run it with:
node_modules/.bin/http-serverWhat if there is already a server at localhost:5000?
http-server -p 5001 or any other unused port numberserve -l tcp://127.0.0.22:2112 where you can put in any suitable IP address for 127.0.0.22 and port for 2112Externally Visible Server
Need to use an externally visible IPv4 address, Use the netIf.js program to find yours.
Use the -c-1 option to turn off caching if desred
Start serve with:
http-server -a yourIPv4Address -p YourPortChoicenode_modules directorynode_modules directory within your project directory.node_modules directory can get very large.
package.json file (to be discussed)package.jsonFrom Using package.json
package.jsonYou can build it by hand:
{
"name": "your-project-name",
"version": "0.0.1"
}Run npm init and npm will ask you questions to build you package.json file.
Run npm init --yes will create a package.json you can later edit without all the questions. Try it!
From using package.json
To specify the packages your project depends on, you need to list the packages you’d like to use in your package.json file. There are 2 types of packages you can list:
package.jsonYou can manually add and delete your projects dependencies, but its much easier to let npm help you.
For a regular package dependency use npm install package_name --save when you install a package.
For a development dependency use npm install package_name --save-dev when you install a development package.
node_modulespackage.json file.package.json file in a directory, just run npm install to re-create your node_modules directory.Required for CS651, Optional for CS351
How can a Node.js based server keep up with servers based on close to the “metal” languages such as C++ and Go
Browser vendors highly optimize JavaScript Execution
Most of the time servers are waiting on file servers and database servers
A different approach to concurrency
No threads or processes (for the programmer)
Instead a model built around events and callbacks
Asynchronous file reading simpleRead.js
// Simple asynchronous file reading
const fs = require('fs'); // File system module
let fname = __dirname + '/hiNode.js';
// Callback for readFile
function processFile(err, data) {
if (err) {
console.log("Some kind of error");
return;
}
console.log(data);
}
// This function takes a callback function as an argument.
fs.readFile(fname, 'utf8', processFile);With a some help from libuv
Full-featured event loop backed by epoll, kqueue, IOCP, event ports.
Asynchronous TCP and UDP sockets
Asynchronous DNS resolution
Asynchronous file and file system operations
Kind of…
In the past blocking operations, separate threads, and/or processes where used per TCP/UDP socket or so…
The NGINX web server (comercial and open source) used this approach to get greatly improved performance over Apache.
The Apache Webserver moved to an event based approach in version 2.4
Python libraries such as eventlet take a similar approach to achieve high performance.