De bedste JavaScript-vejledninger

JavaScript er det mest anvendte script-sprog på Jorden. Og det har det største biblioteksøkosystem af ethvert programmeringssprog.

JavaScript er kernens sprog på nettet og det eneste programmeringssprog, der kan køre i alle større webbrowsere.

Især har JavaScript ingen relation til Java. Tjek JavaScript: Verdens mest misforståede programmeringssprog.

Det officielle navn på JavaScript er ECMAScript defineret under Standard ECMA-262.

Hvis du vil lære mere om JavaScript-sproget, og hvorfor det bruges så meget, skal du læse Quincy Larsons artikel - Hvilket programmeringssprog skal jeg lære først? - eller se denne inspirerende video fra Preethi Kasireddy.

freeCodeCamp har en dybtgående JavaScript-tutorial på YouTube, der lærer dig alt det grundlæggende på bare 3 timer.

Nogle andre gode JavaScript-tutorials:

  • JavaScript til katte
  • Den moderne JavaScript-vejledning
  • Professor Frisbys mest passende guide til funktionel programmering
  • Veltalende Javascript ( kommenteret )
  • Taler Javascript
  • Udforskning af ES6
  • Udemy - Javascript Understanding the Weird Parts ( første 3,5 timer )
  • Funktionel programmering i JavaScript
  • Introduktion til JavaScript: Første trin
  • Douglas Crockfords videoer
  • Moderne JS Cheatsheet
  • De 50 bedste websteder til at lære JavaScript
  • JavaScript-tutorial til Codementor
  • Du har muligvis ikke brug for jQuery

Referencer

  • DevDocs
  • OverAPI JavaScript snydeark
  • ECMA-262
  • Mozilla Developer Network (MDN)

Hurtig JavaScript

  • REPL ( knude )
  • JSBin
  • JSFiddle
  • CodePen
  • CoderPad ( parprogrammering )
  • C9 ( IDE , parprogrammering )
  • Objekt Legeplads ( visualiser objekter )
  • Plunker

Udfordringer

  • Kode krige
  • Hacker-rang
  • Kodningsspil
  • CodeFights
  • ES6 Katas

Selvstudier

  • Codecademy
  • RithmSchool

Øvelser

  • Kodilitet
  • Coderbyte
  • Motion
  • JavaScript30
  • Javascript.com (pluralsight)

Redaktører

  • Visual Studio-kode
  • Atom
  • Sublim tekst
  • Webstorm
  • Beslag

Blogs

  • Perfektion dræber
  • 2alitet
  • JS samling på Medium
  • David Walsh
  • superheltJS

Podcasts

  • JS Jabber

Video tutorials

  • Derek Banas 'Lær JS i en video
  • Derek Banas 'objektorienterede JavaScript

Bøger

  • Hemmelighederne ved JavaScript Ninja
  • Programmering af JavaScript-applikationer
  • Vedligeholdelig JavaScript
  • Læring af JavaScript-designmønstre
  • Airbnb JavaScript-stilvejledning
  • JSDoc
  • Javascript Allonge Six
  • Du kender ikke JS

6 bøger på JavaScript af Kyle Simpson, fra begynder til avanceret.

  • Veltalende Javascript

Fantastic, thorough introduction to the basics and features of JavaScript, complete with in-browser interactive code.

  • Professor Frisby’s Mostly Adequate Guide to Functional Programming

Quite in-depth guide to Functional Programming in JavaScript

  • The JavaScript Way
  • Functional Light JS

Standalone JavaScript engines

Mozilla’s SpiderMonkey, the first JavaScript engine ever written, currently used in Mozilla Firefox.

V8, Google’s JavaScript engine, used in Google Chrome.

Google Apps Script, a cloud-based/server-side interpreter that provides programmatic “macro-like” control of Google Apps services and documents.

Node.js, built on top of V8, a platform which enables server-side applications to be written in JavaScript.

Windows includes JScript, a JavaScript variant in Windows Script Host.

Chakra, a fork of Jscript, is developed by Microsoft and used in their Edge browser.

Mozilla also offers Rhino, an implementation of JavaScript built in Java, typically embedded into Java applications to provide scripting to end users.

WebKit (except for the Chromium project) implements the JavaScriptCore engine.

JavaScript Frameworks

The most frequently used JavaScript Frameworks are React JS, Angular JS, jQuery, and NodeJS. For more details follow this link.

Advantages and Disadvantages of JavaScript

Like with all programming languages, JavaScript has certain advantages and disadvantages to consider. Many of these are related to the way JavaScript is often executed directly in a client's browser. But there are other ways to use JavaScript now that allow it to have the same benefits of server-side languages.

Advantages of JavaScript

  • Speed - JavaScript tends to be very fast because it is often run immediately within the client's browser. So long as it doesn't require outside resources, JavaScript isn't slowed down by calls to a backend server. Also, major browsers all support JIT (just in time) compilation for JavaScript, meaning that there's no need to compile the code before running it.
  • Simplicity - JavaScript's syntax was inspired by Java's and is relatively easy to learn compared to other popular languages like C++.
  • Popularity - JavaScript is everywhere on the web, and with the advent of Node.js, is increasingly used on the backend. There are countless resources to learn JavaScript. Both StackOverflow and GitHub show an increasing amount of projects that use JavaScript, and the traction it's gained in recent years is only expected to increase.
  • Interoperability - Unlike PHP or other scripting languages, JavaScript can be inserted into any web page. JavaScript can be used in many different kinds of applications because of support in other languages like Pearl and PHP.
  • Server Load - JavaScript is client-side, so it reduces the demand on servers overall, and simple applications may not need a server at all.
  • Rich interfaces - JavaScript can be used to create features like drag and drop and components such as sliders, all of which greatly enhance the user interface and experience of a site.
  • Extended Functionality - Developers can extend the functionality of web pages by writing snippets of JavaScript for third party add-ons like Greasemonkey.
  • Versatility - There are many ways to use JavaScript through Node.js servers. If you were to bootstrap Node.js with Express, use a document database like MongoDB, and use JavaScript on the frontend for clients, it is possible to develop an entire JavaScript app from front to back using only JavaScript.
  • Updates - Since the advent of ECMAScript 5 (the scripting specification that JavaScript relies on), ECMA International has been dedicated to updating JavaScript annually. So far, we have received browser support for ES6 in 2017 and look forward to ES7 being supported in the future.

Disadvantages of JavaScript

  • Client-Side Security - Since JavaScript code is executed on the client-side, bugs and oversights can sometimes be exploited for malicious purposes. Because of this, some people choose to disable JavaScript entirely.
  • Browser Support - While server-side scripts always produce the same output, different browsers sometimes interpret JavaScript code differently. These days the differences are minimal, and you shouldn't have to worry about it as long as you test your script in all major browsers.

ES6

The 6th edition of ECMAScript is called ES6.

It is also know as ES2015.

The changes add a lot of syntactic sugar that allow developers to create applications in an object oriented style.

ES5 example:

var User = function () { function User(name) { this._name = name; } User.prototype.getName = function getName(x) { return 'Mr./Mrs. ' + this._name; }; return User; }();

ES6 example:

class User { constructor(name) { this._name = name } getName() { return `Mr./Mrs. ${this._name}` } }

A lot of new syntax features were introduced including:

  • classes
  • modules
  • templating
  • for/of loops
  • generator expressions
  • arrow functions
  • collections
  • promises

Nowadays most of the features are available in all popular browsers. The compatibility table contains all information about feature availability of all modern browsers.

Frequently, new features arrive that are part of the successor ES7. A common way is to translate modern JavaScript (ES6, ES7 and other experimental proposals) to ES5. This makes sure that also old browsers can execute the code. There are tools like Babel that transforms new JavaScript to ES5.

Besides syntactic sugar coming from ECMAScript standards there are features that require a Polyfill. Usually they are necessary because whole class/method implementations were added to the standard.

Object Instantiation

In JavaScript and most other languages, an object contains a series of properties, which are a key, value pair. There are multiple options available to you when you need to construct an object.

Initialize an object variable

You can create an object with pre-defined properties like so:

let myObject = { name: "Dave", age: 33 }

Creating an empty object

Dette skaber et tomt objekt inde i vores myObject-variabel:

let myObject = new Object();

Når du ønsker at tilføje egenskaber til dit objekt, skal du blot bruge enten punktnotation eller parentesnotation med det valgte ejendomsnavn:

myObject.name = "Johnny Mnemonic" myObject["age"] = 55

Brug af en konstruktørfunktion

Du kan definere en konstruktionsfunktion, som du kan bruge til at oprette dine objekter:

function Kitten(name, cute, color) { this.name = name, this.cute = cute, this.color = color }

Du kan definere en variabel, der indeholder en instantiering af dette objekt ved at kalde konstruktorfunktionen:

let myKitten = new Kitten("Nibbles", true, "white")

Object.create ()

Metoden Object.create () (først defineret i ECMAScript 5.1) giver dig mulighed for at oprette objekter. det giver dig mulighed for at vælge prototype-objektet til dit nye objekt uden at skulle definere en konstruktorfunktion på forhånd.

// Our pre-defined object let kitten = { name: "Fluff", cute: true, color: "gray" } // Create a new object using Object.create(). kitten is used as the prototype let newKitten = Object.create(kitten) console.log(newKitten.name) // Will output "Fluff"