YinhaoHe / nodeDevPlayground

Node

What is Node

• Used to run JavaScript code in v8 engine

Everything about Node

• Node is a runtime environment for executing JS code.

• Essentially, Node is a C++ program that embeds Chrome’s v8 engine, the fastest JS engine in the world.

• We use Node to build fast and scalable networking applications. It’s a perfect choice for building RESTful services.

• Node applications are single-threaded. That means a single thread is used to serve all clients.

• Node applications are asynchronous or non-blocking by default. That means when the application involves I/O operations (eg accessing the file system or the network), the thread doesn’t wait (or block) for the result of the operation. It is released to serve other clients.

• This architecture makes Node ideal for building I/O-intensive applications.

• You should avoid using Node for CPU-intensive applications, such as a video encoding service. Because while executing these operations, other clients have to wait for the single thread to finish its job and be ready to serve them.

• In Node, we don’t have browser environment objects such as window or the document object. Instead, we have other objects that are not available in browsers, such as objects for working with the file system, network, operating system, etc.

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Module

Global Object

• global obj in node.js is similar to window obj in browsers.
• In browsers, var message = ''; window.message can be access.
• In Node, var message = ''; global.message CANNOT be access - undefined

console.log(); === global.console.log();

setTimeout(); === global.setTimeout();
clearTimeout();

var message = '';
"global.message" is WRONG

setInterval();
clearInterval();

• There is no window object in node.js. window obj is in browser only.
• window.console.log equals to console.log in browers.

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Modules

• Every file is a module.

• Every project have a main module.

• Do not add function to global, instead design it in a Module.

• Called private in OOP

console.log(module);

//log will show a json file.

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Create a Module

• module.exports.log = log; - export an obj
• module.exports = log; - export a function
• Only export what's needed; hide all details; encapsulation

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Load a Module

• require() - only in Node not in Browsers
• const logger = require("./logger");

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Module Wrapper Function

(function (exports, require, module, __filename, __dirname){
  
})

• Node does not execute code directly, it wraps code in a function.

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Path Module

const path = require("path");

var pathObj = path.parse(__filename);
console.log(pathObj);

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OS Module

const os = require("os");

var totalM = os.totalmem();
var freeM = os.freemem();

// ES6
// Template string
console.log(`Total Memory: ${totalM}`);
console.log(`Free Memory: ${freeM}`);

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File System Module

const fs = require("fs");

fs.readdir("./", (err, files) => {
  if (err) console.log("Error", err);
  else console.log("Result", files);
});

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Event Module

• Listener - to listen and handle an event
• Emit - to raise an event

const EventEmitter = require("events");
const emitter = new EventEmitter();

// Register a listener
emitter.on("messageLogged", () => {
  console.log("Listener called");
});

// Raise an event
emitter.emit("messageLogged");

• emitter.emit - emitter can add arguments
• emitter.on - listener can listen and take the args

const EventEmitter = require("events");
const emitter = new EventEmitter();

// Register a listener
emitter.on("messageLogged", (arg) => {
  console.log("Listener called", arg);
});

// Raise an event
emitter.emit("messageLogged", { id: 1, url: "http://" });

• Extend EventEmitter

logger.js

const EventEmitter = require("events");

var url = "http://mylogger.io/log";

class Logger extends EventEmitter {
  log(message) {
    // Send an HTTP request
    console.log(message);

    // Raise an event
    this.emit("messageLogged", { id: 1, url: "http://" });
  }
}

module.exports = Logger;

app.js

const Logger = require("./logger.js");
const logger = new Logger();

// Register a listener
logger.on("messageLogged", (arg) => {
  console.log("Listener called", arg);
});

logger.log("message");

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HTTP module

• We DO NOT use this to build http server
• We USE Express which is built on HTTP module
• express can better handle the routes instead of writing routes linearly

const http = require("http");

const server = http.createServer((req, res) => {
  if (req.url === "/") {
    res.write("hello world");
    res.end();
  }

  if (req.url === "/api/courses") {
    res.write(JSON.stringify([1, 2, 3]));
    res.end();
  }
});

// http is a EventEmitter too
// server.on("connection", (socket) => {
//   console.log("New connection...");
// });

server.listen(3000);

console.log("Listening on port 3000...");

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Node Core

• We don’t have the window object in Node.
• The global object in Node is “global”.
• Unlike browser applications, variables we define are not added to the “global” object.
• Every file in a Node application is a module. Node automatically wraps the code in each file with an IIFE (Immediately-invoked Function Expression) to create scope. So, variables and functions defined in one file are only scoped to that file and not visible to other files unless explicitly exported.
• To export a variable or function from a module, you need to add them to module.exports: module.exports.sayHello = sayHello;
• To load a module, use the require function. This function returns the module.exports object exported from the target module: const logger = require(‘./logger’);
• Node has a few built-in modules that enable us to work with the file system, path objects, network, operating system, etc.
• EventEmitter is one of the core classes in Node that allows us to raise (emit) and handle events. Several built-in classes in Node derive from EventEmitter.
• To create a class with the ability to raise events, we should extend EventEmitter: class Logger extends EventEmitter { }

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NPM

Resolve a module

require() will resolve the module in the following order:

var _ = require("underscore");

• Core module
• File or folder
• node_modules

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Semantic Versioning

• Major.Minor.Patch
• ^4.13.6 === 4.x.x
• ~1.8.3 === 1.8.x

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Listing the Installed Packages

• npm list - to view every package's and its dependency's version
• npm list --depth=0 - Only to view your packages' dependency

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Viewing Registry info for a Package

• npm view mongoose - to view everything(all the meta data) about this package
• npm view mongoose dependencies - Only to view the dependency
• npm view mongoose versions - To view all the versions of this package

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Installing a Specific Version of a Package

• npm i mongoose@2.4.2 - install the exact version of this package

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Updating Local Packages

• npm outdated - to view the newest package version
• npm update - only update the minor and patch version packages; DOES NOT update Major version update
• npm i -g npm-check-updates - A tool to help with update everything
• After install npm-check-updates, run ncu -u, then run npm i - TO update EVERYTHING

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DevDependencies

• npm i jshint --save-dev - install development dependencies

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Uninstall a Package

• npm un mongoose - to uninstall a package

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Working with Global Packages

• npm i -g npm - install globally
• npm -g outdated - find outdated packages globally

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Publishing a Package

• npm login
• npm publish

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Updating a Published Package

• npm version major - You need to update your version first then publish
• npm publish

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NPM

• Every Node application has a package.json file that includes metadata about the application. This includes the name of the application, its version, dependencies, etc.
• We use NPM to download and install 3rd-party packages from NPM registry:
• All the installed packages and their dependencies are stored under node_modules folders. This folder should be excluded from the source control.
• Node packages follow semantic versioning: major.minor.patch
• Useful NPM commands are:
• Install a package: npm i <packageName>
• Install a specific version of a package: npm i <packageName>@<version>
• Install a package as a development dependency: npm i <packageName> —save-dev
• Uninstall a package: npm un <packageName>
• List installed packages: npm list —depth=0
• View outdated packages: npm outdated
• Update packages: npm update
• To install/uninstall packages globally, use -g flag.

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