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:

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

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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.
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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".
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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.
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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.
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5. == vs === vs typeof

JavaScript has two visually similar, yet very different, ways to test equality. You can test equality with == or ===.
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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.
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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.
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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.”
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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.
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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”.
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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.
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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).
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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.
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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.
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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.
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16. new, Constructor, instanceof and Instances

Every JavaScript object has a prototype. All objects in JavaScript inherit their methods and properties from their prototypes.
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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).
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18. Object.create and Object.assign

The Object.create method is one of the methods to create a new object in JavaScript.
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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.
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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?
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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.
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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.
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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.
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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.
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25. Promises

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

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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.
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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.
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32. Partial Applications, Currying, Compose and Pipe

Function composition is a mechanism of combining multiple simple functions to build a more complicated one.
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33. Clean Code

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