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Learn JavaScript – In Depth

Latest Updates

March 29th, 2024
πŸ₯‹ I released Learning JavaScript Arrays.
Let me know what you think.
March 28th, 2024
πŸ₯‹ The first array.push() kata gave me so many
more ideas for katas on arr.push(), it's a πŸ‡ hole.
March 27th, 2024
πŸ†• The first kata on Object() constructor as a function
January 16th, 2024
πŸ†• πŸ‰ First ES14/ES2023 kata array.toReversed()
November 7th, 2023
πŸ†• First type-conversion kata "to boolean"
November 5th, 2023
πŸ†• 9 new katas around functions 🀯.
πŸ”₯ The first strict mode kata.
πŸ‘·πŸ½β€β™€οΈ Each test runs in a separate worker thread now,
this allows for more test cases to be written.
October 15th, 2023
πŸ†• 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: πŸ†• function.length for ES1 and πŸ†• with ES6 features.
October 11th, 2023
πŸ†• 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
πŸ†• New kata: String.raw.
September 30th, 2023
Dive into JavaScript arrays β€” 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
πŸŽ‰ πŸŽ‰ πŸŽ‰ A Big Change. πŸŽ‰ πŸŽ‰ πŸŽ‰
Now you can solve the katas inline without going to tddbin.
September 4th, 2023
πŸ†• New kata Bitwise Shift Operators: Right Shift ">>"
πŸ†• New kata All bitwise shift operators
September 1st, 2023
πŸ†• New kata Bitwise Shift Operators: Left Shift "<<"

πŸ‘€ 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.

πŸ§›πŸΌ You're a seasoned pro, discover hidden JavaScript gems πŸ’Ž.
For example: Do you know all three bitwise shift operators? πŸ€”

ECMAScript 1 19 katas

Function constructor

Function.length #easy #in progress
Function.prototype #easy #in progress

Type conversion

to number #in progress

Global Object API

parseInt() #easy
parseInt() in depth #easy #in progress

ECMAScript 3 2 katas

ECMAScript 5 4 katas

ECMAScript 6 / ES2015 86 katas


array #easy
defaults #easy
object #easy
string #easy


usage #in progress

Object literal

getter #easy
setter #easy

Template strings

basics #easy
multiline #easy

Spread operator

Block scope

Arrow functions

basics #easy


import statement #easy #in progress

Default parameters

basics #easy

Object API

Object.is() #easy


ECMAScript 7 / ES2016 1 katas

Array API

ECMAScript 8 / ES2017 3 katas

Object API

Object.entries() #easy #in progress
Object.values() #easy #in progress

Async Function

ECMAScript 10 / ES2019 12 katas

Array API

array.flat() #in progress
array.flatMap() #in progress
stable array.sort() #in progress

String API

string.trimEnd() #easy #in progress


unbinded catch #easy #in progress

Symbol API

symbol.description #in progress

JSON superset

JSON superset basics #in progress


well-formed JSON.stringify() #easy #in progress

Function API

function.toString() #easy #in progress

ECMAScript 11 / ES2020 3 katas


basics #easy

ECMAScript 14 / ES2023 1 katas