Node.js

Node

It’s an asynchronous event-driven JS runtime, designed to build scalable network applications

• Actually not a framework…
• Node.js is a runtime environment that allows you to run JavaScript code outside of a browser.

• diagram
• A runtime environment
  • when js was first created, it was designed to run in the browser (impossible to use js for anything not a website).
  • but Node uses the V8 engine (comes from chromium, written in C and C++, VERY fast, powers the chrome browser)
  • Node allows us to use JS outside browsers, maintaining our full JS stack from frontend to backend
• asynchronous, event-driven
  • js code doesn’t have to do everything sequentially
• In summary, we need node because it allows us to build an application on a computer using JS
  • this application will be running on our server (a computer, which is NOT a browser), and Node.js allows that to happen
• You need a deployment platform to host your app so users can access it.
  • AWS, Vercel, etc
• Some redditor
  • https://www.reddit.com/r/learnjavascript/comments/3d4hs5/comment/ct2b9oe/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

Commands

• node -v
• Node REPL (Read Eval Print Loop)
  • A computer environment where user inputs are read and evaluated, and then the results are returned to the user
  • similar to JS console in browser.. we’ve just taken that out of the browser and run it in our pc terminal
  • node
    • .help
    • .exit or Ctrl+C
  • (not unique to node, smth we can do with most programming languages)
• writing a js file and using node to run the entire file
  • node index.js

Native Node Modules

• Your starting tool set. Has TONS of FEATURES for creating applications (esp backend) to be easier
  • file access (reading and writing), networking, etc
  • https://nodejs.org/docs/latest-v18.x/api/index.html
• Built-In Libraries/Modules
  • Core Modules: Node.js comes with a rich set of built-in libraries (e.g., http, fs, path, os, stream, etc.) to handle basic tasks like HTTP requests, file system operations, networking, and more, without needing extra libraries.
  • This means you can create basic web servers, manage files, and do networking tasks without needing third-party libraries.
• NPM (Node Package Manager)
  • NPM is the world’s largest package registry, which means there’s a massive selection of open-source libraries and packages available. You can install packages for anything, like authentication, database integration, utilities, and more.
  • You can use npm to manage dependencies and add functionality to your app easily.
• cross platform

File System

The native node module that allows us to access the local storage

• https://nodejs.org/docs/latest-v18.x/api/fs.html
• remember, with native JS run in the browser, you can’t access a user’s files in their PC
• but now that we can use JS outside the browser, we can read/write files on the server (or local computer)
• ways
  • import the code
  • require the bits that we need from this module

require

const fs = require("")

• module we need needs to be entered as a string

const fs = require("fs");
 
// writes to file
fs.writeFile("message.txt", "Hello node!", (err) => {
  if (err) throw err;
  console.log("File saved!");
});
 
// reads from file
fs.readFile("message.txt", "utf8", (err, data) => {
  if (err) throw err;
  console.log(data);
});
 

• allows us to take a msg (ex. user input) and write it into a file to be saved onto the computer
• writeFile, readFile

Node Package Manager (NPM)

• Native node modules - toolbox we have at home
• NPM (node package manager) - community tool library
  • its open source and you can search to find all the packages that other developers have created
  • comes pre-bundled with node, so if u have node installed you also have npm installed
• initializing first npm project
  • npm init
  • this will create the configurations for our project → package.json
    • similar to how js objects are structured
• we can start installing and using npm packages
  • will be added to dependencies in package.json and a separate folder in node_modules
  • npm install <package1> <package2>
  • npm i <package>
  • https://www.npmjs.com/
• The ECMAScript modules
  • CJS - CommonJS
    • we have to use the “require” keyword
  • ESM - ECMAScript
    • we can use “import” keyword (and whole bunch of behind the scene things)
    • we have to go to package.json and add "type": "module",
    • in the main file, write import generateName from "sillyname";
      • write import xxx from "sillyname"; first, then write the xxx keyword (for autocomplete)
    • you CAN’T mix imports!
• if u copied some project, the node_modules will not be downloaded for u
  • u have to npm install Example task from angela

/* 
1. Use the inquirer npm package to get user input.
2. Use the qr-image npm package to turn the user entered URL into a QR code image.
3. Create a txt file to save the user input using the native fs node module.
*/
 
import input from "@inquirer/input";
import qr from "qr-image";
import fs from "fs";
 
// getting url from user input
const url = await input({ message: "Enter URL" });
 
// save user input to txt file
fs.writeFile("url.txt", url, (err) => {
  if (err) throw err;
  console.log("file saved!");
});
 
// creating the qr image from user entered url
const qr_img = qr.image(url);
qr_img.pipe(fs.createWriteStream("i_love_qr.png"));