nodejs

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node js

nodejs

As an asynchronous event-driven JavaScript runtime, Node.js is designed to build scalable network applications

nodejs is a javascript runtime which allows you to execute server side javascript scripts and applications

The most basic javascript script

write script into file script.js

execute script

console output

nodejs ships with a big standard library which covers a lot of filesystem, text processing and network APIs

In addition to the standard library nodejs ships with a built-in package management system which allow you to install 3rd party packages to extend the functionality of the standard library

nodejs is based googles V8 javascript engine and thus has the same limitations regarding threading behavior as the browser engine

Disclaimer: Just because of nodejs is capable of doing a task its not always the best tool

nodejs packages

Important: because nodejs supports ES Modules, I will only use the ES module syntax and don't dive into commonjs

A nodejs packages consists of a directory which has at least on file

• package.json this file is mandatory and describes the package
• <filename>.js an arbitrary number of javascript modules
• node_modules folder for dependencies (only after installing)

A simple package description

name of the package

type of the javascript files inside the package, in this case es modules

version of the package, must comply semantic versioning standard

main entry point for bare imports

description of the package

object with a list of packages our package depends on

sample content of index.js file

import a function provided by the standard library (built-in module)

bare import a function provided by a third party packages (located in node_modules)

relative import a function from a module of your package

export a function to be used by other modules or packages

creation of new package, create a folder and run npm init within the folder and follow the instructions

In general there are two types of packages, library packages which provides additional functionality and only exports functions, constants, etc.. and application packages which contain an application which can be run directly

npm and dependencies

nodejs brings its own tool for managing packages and dependencies, also there is a global registry provided under https://www.npmjs.com/ where you can publish your own packages and get 3rd party packages

npm is the built in command line utility for node to manage and install packages and dependencies

To install a new package you just have to execute npm install <package>@<version> within your package where the package.json file is located

the <version> path can be omitted if you want the latest published version

You can also manually edit the package.json file and add dependencies

packages which your package depends upon will be saved to the node_modules folder next to your package.json. The node package resolution algorithm will scan this folder if you use a bare import within your javascript

node packages have three types depdendencies

dependencies are runtime dependencies which are needed during the execution of your package

devDependencies are dependencies which are needed only during the development of your package or for building it

typescript, module bundler, linter, etc... for example

peerDependencies are dependencies which are provided by the consumer of your package

usually used if you write a plugin to a library, then the consumer must add the package your library extends

The dependency objects are key value pairs with the package name as key and the version as value

In this case the package depends on the package ws with version [7.3.0, 8.0.0)

A simple Webserver with nodejs

create a folder and a package.json file

add module type to package.json

open index.js and create a new webserver

import the http package from the standard library

define the host on which the server listens and a port

create a new server and listen to requests

create a response to every requests which resturns 'hello world'

start server

If we now start the server and try to access it we get 'hello world' as a response

Now we want top be able to serve static files

import helpers for file system access and path handling

we parse the provided url and rewrite it to "index.html" if no path provided

We need to make tha paths relative passed as an url, so we need to remove the leading /

If the file exists we read it and return the content in the response

Now if we create a index.html within our project and navigate to http://127.0.0.1:3000 the index.html will be displayed in a browser

Until now we only support html files, we need to add a function to determine the right MIME-Type and return it as Content-Type

We need to determine the content type by the provided file extension

return the correct mime type for a specific file extension

we can also overwrite specific paths to return the greeting from the first example

unfortunately nodejs does not support websockets out of the box so we need to add a 3rd party library

because the ws package is a older commonjs module we can import it but we need to access the exports via the "default" property

to establish a websocket connection we forward an "upgrade" request to our websocketServer which will create a small echo service