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Learn JavaScript – In Depth

Topics 133 katas

Object API 7

Object.groupBy() #new
Object() (as introduced in ES1)
Object.entries() #in progress
Object.fromEntries()
Object.fromEntries() in depth
Object.is()
Object.values() #in progress

Proxy 1

basics #new

Array API 18

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.push() (as introduced in ES3)
array.shift() (as introduced in ES3)
array.sort() basics
array.sort() can take a compare function
array.toReversed()
array.values()
stable array.sort() #in progress
📕 Learning JavaScript Arrays

function API 9

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

String API 9

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

Class 7

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

Generator 6

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

Destructuring 6

array
assign
defaults
object
parameters
string

Promise 5

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

Reflect 5

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

Set 5

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

Map 5

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

Iterator 4

array
protocol
string
usage #in progress

Symbol 4

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

Object literal 4

basics
computed properties
getter
setter

Template strings 4

raw property
basics
multiline
tagged template strings

Function constructor 3

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

Bitwise Shift Operators 3

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

Unary Operators 4

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

Number API 4

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

Type conversion 2

to boolean
to number #in progress

Global Object API 3

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

Spread operator 2

with arrays
with strings

Rest operator 2

as parameter
with destructuring

Block scope 2

const declaration
let declaration

Arrow functions 2

basics
function binding

Strict mode 2

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

Modules 1

import statement #in progress

Default parameters 1

basics

Unicode 1

in strings

Async Function 1

basics

try-catch 1

unbinded catch #in progress

Symbol API 1

symbol.description #in progress

JSON superset 1

JSON superset basics #in progress

JSON API 1

well-formed JSON.stringify() #in progress

Function API 1

function.toString() #in progress

BigInt 1

basics

👀 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 💎.
For example: Do you know all three bitwise shift operators? 🤔

Latest Updates

October 18th, 2024
🥋 The first Proxy basics kata inspired by the 76th #JSLang meetup
March 29th, 2024
🥋 I released Learning JavaScript Arrays.
Let me know what you think.
March 28th, 2024
🥋 The first array.push() kata gave me so many
more ideas for katas on arr.push(), it's a 🐇 hole.
March 27th, 2024
🆕 The first kata on Object() constructor as a function
January 16th, 2024
🆕 🍉 First ES14/ES2023 kata array.toReversed()
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 "<<"