33 JavaScript Concepts Every Developer Should Know 🤓️💯️

How much of JavaScript do you really think you know? You probably know how to write functions, understand simple algorithms, and can even write a class. But do you know what a typed array is?

You don't need to know all of these concepts right now, but you will eventually need them later in your career. That’s why I recommend bookmarking this list, because chances are, you’ll encounter one of these topics, and then you’re gonna want a tutorial to fully understand it.

It’s important to note that this list was inspired from the following repository:

leonardomso / 33-js-concepts

📜 33 JavaScript concepts every developer should know.

33 Concepts Every JavaScript Developer Should Know

Introduction

This repository was created with the intention of helping developers master their concepts in JavaScript. It is not a requirement, but a guide for future studies. It is based on an article written by Stephen Curtis and you can read it here.

🚀 Considered by GitHub as one of the top open source projects of 2018!

Community

Feel free to submit a PR by adding a link to your own recaps or reviews. If you want to translate the repo into your native language, please feel free to do so.

All the translations for this repo will be listed below:

• اَلْعَرَبِيَّةُ‎ (Arabic) — Amr Elsekilly
• Български (Bulgarian) - thewebmasterp
• 汉语 (Chinese) — Re Tian
• Português do Brasil (Brazilian Portuguese) — Tiago Boeing
• 한국어 (Korean) — Suin Lee
• Español (Spanish) — Adonis Mendoza
• Türkçe (Turkish) — İlker Demir
• русский язык (Russian) —…

View on GitHub

Please give the author and contributors of the 33 JS Concepts repository some love for gathering this amazing list of resources! ❤️

So without further ado, let’s begin!

Table of Contents

1. Call Stack
2. Primitive Types
3. Value Types and Reference Types
4. Implicit, Explicit, Nominal, Structuring and Duck Typing
5. == vs === vs typeof
6. Function Scope, Block Scope and Lexical Scope
7. Expression vs Statement
8. IIFE, Modules and Namespaces
9. Message Queue and Event Loop
10. setTimeout, setInterval and requestAnimationFrame
11. JavaScript Engines
12. Bitwise Operators, Type Arrays and Array Buffers
13. DOM and Layout Trees
14. Factories and Classes
15. this, call, apply and bind
16. new, Constructor, instanceof and Instances
17. Prototype Inheritance and Prototype Chain
18. Object.create and Object.assign
19. map, reduce, filter
20. Pure Functions, Side Effects, State Mutation and Event Propagation
21. Closures
22. High Order Functions
23. Recursion
24. Collections and Generators
25. Promises
26. async/await
27. Data Structures
28. Expensive Operation and Big O Notation
29. Algorithms
30. Inheritance, Polymorphism and Code Reuse
31. Design Patterns
32. Partial Applications, Currying, Compose and Pipe
33. Clean Code

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1. Call Stack

A call stack is a mechanism for an interpreter (like the JavaScript interpreter in a web browser) to keep track of its place in a script that calls multiple functions — what function is currently being run and what functions are called from within that function, etc.
—Source

Tutorials

• 📜 Understanding Javascript Call Stack, Event Loops — Gaurav Pandvia
• 📜 Understanding the JavaScript Call Stack — Charles Freeborn
• 📜 Javascript: What Is The Execution Context? What Is The Call Stack? — Valentino Gagliardi

2. Primitive Types

All types except objects define immutable values (that is, values which can't be changed). For example (and unlike in C), Strings are immutable. We refer to values of these types as "primitive values".
—Source

Tutorials

• 📜 How numbers are encoded in JavaScript — Dr. Axel Rauschmayer
• 📜 What You Need to Know About JavaScript Number Type — Max Wizard K
• 📜 What Every JavaScript Developer Should Know About Floating Point Numbers — Chewxy

3. Value Types and Reference Types

Variables that are assigned a non-primitive value are given a reference to that value. That reference points to the object’s location in memory. The variables don’t actually contain the value.
—Source

Tutorials

• 📜 Explaining Value vs. Reference in Javascript — Arnav Aggarwal
• 📜 Primitive Types & Reference Types in JavaScript — Bran van der Meer
• 📜 Value Types, Reference Types and Scope in JavaScript — Ben Aston

4. Implicit, Explicit, Nominal, Structuring and Duck Typing

Type coercion means that when the operands of an operator are different types, one of them will be converted to an "equivalent" value of the other operand's type.
—Source

Tutorials

• 📜 What you need to know about Javascript's Implicit Coercion — Promise Tochi
• 📜 JavaScript Type Coercion Explained — Alexey Samoshkin
• 📜 Javascript Coercion Explained — Ben Garrison

5. == vs === vs typeof

JavaScript has two visually similar, yet very different, ways to test equality. You can test equality with == or ===.
—Source

Tutorials

• 📜 JavaScript Double Equals vs. Triple Equals — Brandon Morelli
• 📜 Should I use === or == equality comparison operator in JavaScript? — Panu Pitkamaki
• 📜 == vs === JavaScript: Double Equals and Coercion — AJ Meyghani

6. Function Scope, Block Scope and Lexical Scope

It is important to make this distinction because expressions can act like statements, which is why we also have Expression statements. Though, on other the hand, statements cannot act like expressions.
—Source

Tutorials

• 📜 JavaScript Functions—Understanding The Basics — Brandon Morelli
• 📜 The battle between Function Scope and Block Scope — Marius Herring
• 📜 Emulating Block Scope in JavaScript — Josh Clanton

7. Expression vs Statement

It is important to make this distinction because expressions can act like statements, which is why we also have Expression statements. Though, on other the hand, statements cannot act like expressions.
—Source

Tutorials

• 📜 All you need to know about Javascript's Expressions, Statements and Expression Statements — Promise Tochi
• 📜 Function Expressions vs Function Declarations — Paul Wilkins
• 📜 JavaScript Function — Declaration vs Expression — Ravi Roshan

8. IIFE, Modules and Namespaces

One of the often used coding patterns with functions has got a fancy name for itself: Immediately-invoked Function Expression. Or more dearly known as IIFE and pronounced as “iffy.”
—Source

Tutorials

• 📜 Mastering Immediately-Invoked Function Expressions ― Chandra Gundamaraju
• 📜 Do ES6 Modules make the case of IIFEs obsolete?
• 📜 A 10 minute primer to JavaScript modules, module formats, module loaders and module bundlers ― Jurgen Van de Moere

9. Message Queue and Event Loop

“How is JavaScript asynchronous and single-threaded ?” The short answer is that JavaScript language is single-threaded and the asynchronous behaviour is not part of the JavaScript language itself, rather they are built on top of the core JavaScript language in the browser (or the programming environment) and accessed through the browser APIs.
—Source

Tutorials

• 📜 JavaScript Event Loop Explained — Anoop Raveendran
• 📜 The JavaScript Event Loop: Explained — Erin Sweson-Healey
• 📜 Understanding JS: The Event Loop — Alexander Kondov

10. setTimeout, setInterval and requestAnimationFrame

We may decide to execute a function not right now, but at a certain time later. That’s called “scheduling a call”.
—Source

Tutorials

• 📜 setTimeout and setInterval — JavaScript.Info
• 📜 Why not to use setInterval — Akanksha Sharma
• 📜 setTimeout VS setInterval — Develoger

11. JavaScript Engines

Writing code for the Web sometimes feels a little magical in that developers write a sequence of characters and like magic, those characters turn into concrete images, words, and actions within a browser. Understanding the technology can help developers better tune their craft as programmers.
—Source

Tutorials

• 📜 JavaScript Engines — Jen Looper
• 📜 Understanding How the Chrome V8 Engine Translates JavaScript into Machine Code — DroidHead
• 📜 Understanding V8’s Bytecode — Franziska Hinkelmann

12. Bitwise Operators, Type Arrays and Array Buffers

Okay, so technically for the computer everything goes down to 1s and 0s. It does not operate with digits or characters or strings, it uses only binary digits (bits). The short version of this explanation is that everything is stored in binary form. Then the computer uses encodings such as UTF-8 to map the saved bit combinations to characters, digits or different symbols (the ELI5 version).
—Source

Tutorials

• 📜 Programming with JS: Bitwise Operations — Alexander Kondov
• 📜 Using JavaScript’s Bitwise Operators in Real Life — ian m
• 📜 JavaScript Bitwise Operators — w3resource

13. DOM and Layout Trees

The Document Object Model, usually referred to as the DOM, is an essential part of making websites interactive. It is an interface that allows a programming language to manipulate the content, structure, and style of a website. JavaScript is the client-side scripting language that connects to the DOM in an internet browser.
—Source

Tutorials

• 📜 How To Understand and Modify the DOM in JavaScript — Tania Rascia
• 📜 What’s the Document Object Model, and why you should know how to use it — Leonardo Maldonado
• 📜 JavaScript DOM Tutorial with Example — Guru99

14. Factories and Classes

JavaScript is a prototype-based language, meaning object properties and methods can be shared through generalized objects that have the ability to be cloned and extended. This is known as prototypical inheritance and differs from class inheritance.
—Source

Tutorials

• 📜 How To Use Classes in JavaScript — Tania Rascia
• 📜 Javascript Classes — Under The Hood — Majid
• 📜 ES6 Classes — Nathaniel Foster

15. this, call, apply and bind

These functions are very important for every JavaScript Developer and are used in almost every JavaScript Library or Framework.
—Source

Tutorials

• 📜 Grokking call(), apply() and bind() methods in JavaScript — Aniket Kudale
• 📜 How-to: call() , apply() and bind() in JavaScript — Niladri Sekhar Dutta
• 📜 JavaScript’s Apply, Call, and Bind Methods are Essential for JavaScript Professionals — Richard Bovell

16. new, Constructor, instanceof and Instances

Every JavaScript object has a prototype. All objects in JavaScript inherit their methods and properties from their prototypes.
—Source

Tutorials

• 📜 JavaScript For Beginners: the ‘new’ operator — Brandon Morelli
• 📜 Let’s demystify JavaScript’s ‘new’ keyword — Cynthia Lee
• 📜 Constructor, operator "new" — JavaScript.Info

17. Prototype Inheritance and Prototype Chain

JavaScript is a bit confusing for developers experienced in class-based languages (like Java or C++), as it is dynamic and does not provide a class implementation per se (the class keyword is introduced in ES2015, but is syntactical sugar, JavaScript remains prototype-based).
—Source

Tutorials

• 📜 Javascript : Prototype vs Class — Valentin PARSY
• 📜 JavaScript engine fundamentals: optimizing prototypes — Mathias Bynens
• 📜 JavaScript Prototype — NC Patro

18. Object.create and Object.assign

The Object.create method is one of the methods to create a new object in JavaScript.
—Source

Tutorials

• 📜 Object.create in JavaScript — Rupesh Mishra
• 📜 Object.create(): the New Way to Create Objects in JavaScript — Rob Gravelle
• 📜 Basic Inheritance with Object.create — Joshua Clanton

19. map, reduce, filter

Even if you don’t know what functional programming is you’ve probably been using map, filter and reduce just because they’re so incredibly useful and make your code stink less by allowing you to write cleaner logic.
—Source

Tutorials

• 📜 JavaScript Functional Programming — map, filter and reduce — Bojan Gvozderac
• 📜 Learn map, filter and reduce in Javascript — João Miguel Cunha
• 📜 JavaScript’s Map, Reduce, and Filter — Dan Martensen

20. Pure Functions, Side Effects, State Mutation and Event Propagation

So many of our bugs are rooted in IO related, data mutation, side effect bearing code. These creep up all over our code base—from things like accepting user inputs, receiving an unexpected response via an http call, or writing to the file system. Unfortunately, this is a harsh reality that we should grow accustomed to dealing with. Or is it?
—Source

Tutorials

• 📜 Javascript and Functional Programming — Pure Functions — Omer Goldberg
• 📜 Master the JavaScript Interview: What is a Pure Function? — Eric Elliott
• 📜 JavaScript: What Are Pure Functions And Why Use Them? — James Jeffery

21. Closures

A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function's scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.
—Source

Tutorials

• 📜 I never understood JavaScript closures — Olivier De Meulder
• 📜 Understand JavaScript Closures With Ease — Richard Bovell
• 📜 Understanding JavaScript Closures — Codesmith

22. High Order Functions

JavaScript can accept higher-order functions. This ability to handle higher-order functions, among other characteristics, makes JavaScript one of the programming languages well-suited for functional programming.
—Source

Tutorials

• 📜 Higher-Order Functions in JavaScript — M. David Green
• 📜 Higher Order Functions: Using Filter, Map and Reduce for More Maintainable Code — Guido Schmitz
• 📜 First-class and Higher Order Functions: Effective Functional JavaScript — Hugo Di Francesco

23. Recursion

Consider this post as a series of learning exercises. These examples are designed to make you think — and, if I’m doing it right, maybe expand your understanding of functional programming a little bit.
—Source

Tutorials

• 📜 Recursion in JavaScript — Kevin Ennis
• 📜 Understanding Recursion in JavaScript — Zak Frisch
• 📜 Learn and Understand Recursion in JavaScript — Brandon Morelli

24. Collections and Generators

The Generator object is returned by a generator function and it conforms to both the iterable protocol and the iterator protocol.
—Source

Tutorials

• 📜 ES6 In Depth: Collections — Jason Orendorff
• 📜 ES6 Collections: Using Map, Set, WeakMap, WeakSet — Kyle Pennell
• 📜 ES6 WeakMaps, Sets, and WeakSets in Depth — Nicolás Bevacqua

25. Promises

The Promise object represents the eventual completion (or failure) of an asynchronous operation and its resulting value.
—Source

Tutorials

• 📜 JavaScript Promises for Dummies ― Jecelyn Yeen
• 📜 Understanding promises in JavaScript — Gokul N K
• 📜 Master the JavaScript Interview: What is a Promise? — Eric Elliott

26. async/await

There’s a special syntax to work with promises in a more comfortable fashion, called “async/await”. It’s surprisingly easy to understand and use.
—Source

Tutorials

• 📜 Understanding async/await in Javascript — Gokul N K
• 📜 Exploring Async/Await Functions in JavaScript — Alligator.io
• 📜 Asynchronous Javascript using async/await — Joy Warugu

27. Data Structures

Javascript is evolving each day. With the rapid growth of frameworks and platforms like React, Angular, Vue, NodeJS, Electron, React Native, it has become quite common to use javascript for large-scale applications.
—Source

Tutorials

• 📜 Data Structures in JavaScript — Thon Ly
• 📜 Algorithms and Data Structures in JavaScript — Oleksii Trekhleb
• 📜 Data Structures: Objects and Arrays ― Chris Nwamba

28. Expensive Operation and Big O Notation

“What is Big O Notation?” that is a very common job interview question for developers. In short, it is the mathematical expression of how long an algorithm takes to run depending on how long is the input, usually talking about the worst case scenario.
—Source

Tutorials

• 📜 Big O Notation in Javascript — César Antón Dorantes
• 📜 Time Complexity/Big O Notation — Tim Roberts
• 📜 Big O in JavaScript — Gabriela Medina

29. Algorithms

In mathematics and computer science, an algorithm is a finite sequence of well-defined instructions, typically used to solve a class of specific problems or to perform a computation.

Tutorials

• 📜 Data Structures and Algorithms using ES6
• 📜 Algorithms and data structures implemented in JavaScript with explanations and links to further readings
• 📜 JS: Interview Algorithm

30. Inheritance, Polymorphism and Code Reuse

Class inheritance is a way for one class to extend another class, so we can create new functionality on top of the existing.
—Source

Tutorials

• 📜 Inheritance in JavaScript — Rupesh Mishra
• 📜 Simple Inheritance with JavaScript — David Catuhe
• 📜 JavaScript — Inheritance, delegation patterns and Object linking — NC Patro

31. Design Patterns

Every developer strives to write maintainable, readable, and reusable code. Code structuring becomes more important as applications become larger. Design patterns prove crucial to solving this challenge - providing an organization structure for common issues in a particular circumstance.
—Source

Tutorials

• 📜 4 JavaScript Design Patterns You Should Know — Devan Patel
• 📜 JavaScript Design Patterns – Beginner's Guide to Mobile Web Development — Soumyajit Pathak
• 📜 JavaScript Design Patterns — Akash Pal

32. Partial Applications, Currying, Compose and Pipe

Function composition is a mechanism of combining multiple simple functions to build a more complicated one.
—Source

Tutorials

• 📜 Use function composition in JavaScript — Rémi
• 📜 Currying in JavaScript ES6 — Adam Bene
• 📜 Composition and Currying Elegance in JavaScript — Pragyan Das

33. Clean Code

Writing clean, understandable, and maintainable code is a skill that is crucial for every developer to master.
—Source

Tutorials

• 📜 Clean Code Explained – A Practical Introduction to Clean Coding for Beginners — freeCodeCamp
• 📜 Clean Code concepts adapted for JavaScript — Ryan McDermott
• 📜 Clean Code Practice: How to write clean code — Tirth Bodawala

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If you found this list useful, don’t forget to bookmark it and to follow me for more content like this.

[Deleted User]

Comments

[Medea]

Nice!

[VIDOVA.ai]

❤️

[xiaohuoni]

Can I translate it into Chinese? I will indicate the original link.

[VIDOVA.ai]

yep!

[Shin Messiah]

Very nice selection!

[VIDOVA.ai]

Thanks! 🤗

[Hauke T.]

A nice collection BUT.

Please carefully check your links and resources. I will dismiss any applicant that uses var or iffies without a very good reason. Articles that aim to extend knowledge should not use outdated syntax and especially not promote obsolete/legacy practices. The links regarding Design patterns are so outdated you could run them in IE6.

PLEASE don't promote legacy practices. Junior developers come here to seek best practices. These links teach ancient history.

[Václav Keil]

Hi, Good point! They probably reused an old post...

[Robson Muniz]

Nice Selection!

[Bobo Brussels]

Cool!

[Aditya Singh]

Very nicely explained!

[Nathan Orris]

Oh wow. This is pretty impressive, thanks for your hard work!

[nouman shah]

Cool! :)

[thangdangblog]

Thank you for your post!