jskatas.org Continuously Learn JavaScript. Your Way.

Learn JavaScript – Test-Driven

👀 You're a newbie, JSKatas takes you by the hand and helps you learn at your speed! Start with an easy kata to get the hang of it and find out if you like it. For example learn how to declare a variable.

🧛🏼 You're a seasoned pro, discover hidden JavaScript gems 💎.
Do you know all three bitwise shift operators? 🤔

🚀 You feel like you're ready to learn Arrays? This course cover the creation of an array all the way to how to filter 🔍, convert 🙅🏼‍♂️, map 📍, reduce ♻️ and sort ✔️ arrays. Arrays are everywhere.

⏰ You want to learn all of JavaScript, even ECMAScript1?
Find all chronologically sorted katas here.

Latest Updates

November 7th, 2023
🆕 First type-conversion kata "to boolean"
November 5th, 2023
🆕 9 new katas around functions 🤯.
🔥 The first strict mode kata.
👷🏽‍♀️ Each test runs in a separate worker thread now,
this allows for more test cases to be written.
October 15th, 2023
🆕 NEW: function.name kata.
🌟 Two katas in progress: Symbol.hasInstance and function.name in depth.
October 14th, 2023
✨ Add 'How to' on the kata pages.
🧹 Improved class-creation kata. Explains better, covers more knowledge.
Two new katas: 🆕 function.length for ES1 and 🆕 with ES6 features.
October 11th, 2023
🆕 array.shift() first introduced in 1999, has a kata now.
The kata for let is now in GIVEN-WHEN-THEN style for better usability.
October 9th, 2023
🐞 Bugfix: Make the let kata work again, it runs in a worker thread now (see issue).
October 8th, 2023
🆕 New kata: String.raw.
September 30th, 2023
Dive into JavaScript arrays — the first in-depth article in our series!
September 29th, 2023
Configure the behavior on the kata site, turn on/off the auto-open of the first kata, and more.
September 26th, 2023
🎉 🎉 🎉 A Big Change. 🎉 🎉 🎉
Now you can solve the katas inline without going to tddbin.
September 4th, 2023
🆕 New kata Bitwise Shift Operators: Right Shift ">>"
🆕 New kata All bitwise shift operators
September 1st, 2023
🆕 New kata Bitwise Shift Operators: Left Shift "<<"

Topics 128 katas

Array API

array.entries()
array.fill()
array.find()
array.findIndex()
array.flat() #in progress
array.flatMap() #in progress
Array.from()
array.includes()
array.keys()
Array.of()
array.shift() #new
array.sort() basics
array.sort() can take a compare function
array.values()
stable array.sort() #in progress
📕 Learning JavaScript Arrays

String API

string.endsWith()
string.includes()
string.matchAll()
string.matchAll() in depth #in progress
String.raw #new
string.repeat(count)
string.startsWith()
string.trimEnd() #in progress
string.trimStart()

function API

function.arguments (as modified since ES5) #in progress
function.arguments (as per ES1 spec) #in progress
function.bind() #new
function.length (as per ES1 spec) #new
function.length (with ES5 features) #new
function.length (with ES6 features) #new
function.name #new
function.name in depth #in progress
function.prototype #in progress

Class

accessors
creation
extends
more extends
static
super in constructor
super in method

Destructuring

array
assign
defaults
object
parameters
string

Generator

return inside a generator function
creation
iterator
send function to a generator
send value to a generator
yield expressions

Object API

Object.entries() #in progress
Object.fromEntries()
Object.fromEntries() in depth
Object.is()
Object.values() #in progress

Map

map.get()
map.has()
map.set()
Basics
initialize

Set

set.add()
set.clear()
set.delete()
basics
the API

Reflect

Reflect.apply()
Reflect.construct()
Reflect.defineProperty()
Reflect.getPrototypeOf()
Basics

Promise

promise.catch()
basics
chaining then()
creation
the API

Template strings

raw property
basics
multiline
tagged template strings

Object literal

basics
computed properties
getter
setter

Symbol

Symbol.for()
Symbol.hasInstance method #in progress
Symbol.keyFor()
basics

Iterator

array
protocol
string
usage #in progress

Number API

Number.isInteger()
Number.isNaN()
Number.parseInt()
📕 Building the parseInt() Katas

Unary Operators

All unary operators
Unary "+" operator
Unary "+" operator in depth
📕 What's an "Unary" Operator?

Bitwise Shift Operators

All bitwise shift operators
Left Shift "<<"
Right Shift ">>"

Function constructor

Function.length #in progress
Function.prototype #in progress
new Function() and Function() #in progress

Arrow functions

basics
function binding

Block scope

const declaration
let declaration

Rest operator

as parameter
with destructuring

Spread operator

with arrays
with strings

Global Object API

parseInt()
parseInt() in depth #in progress
📕 Building the parseInt() Katas

Type conversion

to boolean #new
to number #in progress

BigInt

Basics

Function API

function.toString() #in progress

JSON API

well-formed JSON.stringify() #in progress

JSON superset

JSON superset basics #in progress

Symbol API

symbol.description #in progress

try-catch

unbinded catch #in progress

Async Function

basics

Unicode

in strings

Default parameters

Basics

Modules

import statement #in progress

Strict mode

Turn strict mode on/off #new
📕 How to Control Strict Mode