abc-notepedia

# Node Modules

  • Code can be organized into separate files, modules, and combined through requiring them where needed using the require() function.
  • In addition to core modules, modules included within the environment to efficiently perform common tasks, we can also create our own modules using module.exports and the require() function.

Modularity - separate the program into manageable chunks.

Code is organized into separate files and combined through requiring them where needed using the require() function.

core modules - part of node.

// Require in the 'events' core module:
let events = require('events');

require() can also be used for own creations:

The require() function will first check if its argument is a core module, if not, it will move try to locate it

https://nodejs.org/api/modules.html#modules_modules

  • core modules: name of the module as a string
  • local modules: path to the module

It assumes file extensions if none are provided:

let Dog = require('./dog.js');

let Dog = require('./dog'); works as well

// app.js
let Dog = require('./dog.js');
const lumpi = new Dog('Lumpi');
console.log(lumpi.praise());

// dog.js
module.exports = class Dog {
  constructor(name) {
    this.name = name;
  }
 
  praise() {
    return `Good dog, ${this.name}!`;
  }
};
# module.exports.

holds everything in that file, or module, that’s available to be required into a different file.

# Importing and creating modules (opens new window)

A module is a JavaScript library/file that you can import into other code using Node's require() function.

  • First we invoke the require() function with the name of the module
  • then calling the returned object to create an Express application (opens new window). We can then access the properties and functions of the application object.

Tip: You will want to create your own modules. this allows you to organise your code into manageable parts — a monolithic single-file application is hard to understand and maintain. Using modules also helps you manage your namespace, because only the variables you explicitly export are imported when you use a module.

To make objects available outside of a module you just need to expose them as additional properties on the exports object.

exports.area = function(width) { return width * width; };
exports.perimeter = function(width) { return 4 * width; };

We can import this module using require(), and then call the exported method(s)

const square = require('./square'); // Here we require() the name of the file without the (optional) .js file extension
console.log('The area of a square with a width of 4 is ' + square.area(4));

Note: You can also specify an absolute path to the module

can also be done in one assignement:

module.exports = {
  area: function(width) {
    return width * width;
  },

  perimeter: function(width) {
    return 4 * width;
  }
};

Modules-Links

  • https://nodejs.org/api/modules.html#modules_modules

# Module: Nodemon

npm i -D nodemon

then change the start-script in package.json:

 "scripts": {
    "start": "nodemon app.js",

You could install nodemon globally if you wanted (this is NOT required though - because we can just run it locally)

https://www.npmjs.com/package/nodemon

type rs in Terminal forces nodemon to restart

# HTTP Module

  • The Node http core module allows for easy creation of web servers, computer processes that listen for requests from clients and return responses.

http module. This module contains functions which simplify interacting with HTTP and streamline receiving and responding to requests.

  • The http.createServer() method returns an instance of an http.server.
  • An http.server has a method .listen() which causes the server to “listen”

When we run http.createServer() we pass in a custom callback function (often referred to as the requestListener). This callback function will be triggered once the server is listening and receives a request.

https://nodejs.org/api/http.html

# http-module

Launch a server, send requests

http.createServer

takes a request listener as an argument

request listener = function that will run for every incoming request

const http = require('http');

function rqListener(req, res) {
 // funtion runs on every request
}

http.createServer(rqListener)

ore use anonymous function

const http = require('http');

http.createServer((req, res) => {
    // funtion runs on every request
});

this is the createServer-callback

# The server

const http = require('http');

const server = http.createServer((req, res) => {
  console.log(req);
});

server.listen(3000);

← Node Filesystem & Streams →