Step 2 of 2 · your path

JavaScript, Beginner

Start at the bottom of the ladder — what the engine does with your code before line 1 runs, why one thread is enough, and then types, values, operators and functions.

Start reading Change level All chapters

Your progress

0 / 18 done

Up next

Setup & mental model

8 min read · 1 exercise

The way18 chapters

The order I'd read them in

About 2 h 33 min of reading. Tick off what you've read, it is remembered on this device.

⚑ you are here
Setup & mental modelThe layer everybody skips — and it shows in interviews.
8 min read1 exercise
1 exercise
- Fix the temporal dead zone bug9 tests · beginner
Execution contextWhat JavaScript does with your code before it runs a single line of it.
11 min read2 exercises
2 exercises
- Build the creation-phase snapshot8 tests · beginner
- Walk the scope chain8 tests · beginner
var, let and constThree keywords, four questions they answer differently — where a name lives, when you can touch it, whether it can change, and whether you can declare it twice.
14 min read2 exercises
2 exercises
- Would this scope even parse?8 tests · beginner
- Make const mean it8 tests · beginner
ScopeWhich names a line of code can see, why that is decided by where you wrote it, and how JavaScript finds a name — for reading and for writing.
15 min read2 exercises
2 exercises
- Which scope does this name mean?8 tests · beginner
- Where does this assignment land?8 tests · beginner
One thread, one stackWhy JavaScript can only do one thing at a time — and how it still does ten.
10 min read2 exercises
2 exercises
- Read a stack trace back into a stack8 tests · beginner
- Chunk a long job so it stops blocking8 tests · beginner
Inside the browserFrom a script tag to pixels on screen — and where your code sits in that.
8 min read2 exercises
2 exercises
- Predict what runs when8 tests · beginner
- Count the frames you dropped8 tests · beginner
Types & valuesEight types, one conversion table, and the equality check that never stops mattering.
9 min read3 exercises
3 exercises
Strings, numbers & MathThe everyday toolbox every other chapter quietly assumes you already have.
5 min read3 exercises
3 exercises
Operators & flowEvery operator here has an interview question hiding behind it.
11 min read1 exercise
1 exercise
- Defaults that respect 08 tests · beginner
FunctionsA function is a value first, a block of code second.
7 min read2 exercises
2 exercises
- Find the line break that ate the return value9 tests · beginner
- Sum any number of arguments10 tests · beginner
Objects & arraysThe two shapes almost everything you build is made of.
8 min read2 exercises
2 exercises
- Total up a shopping cart10 tests · beginner
- Format an address, safely10 tests · beginner
The this keywordNot where it was written — who called it.
6 min read2 exercises
2 exercises
- Borrow a method using only the dot8 tests · beginner
- A method that survives being detached8 tests · beginner
ClosuresThe function that walked out with its birthplace still attached.
8 min read2 exercises
2 exercises
- A counter nobody can cheat8 tests · beginner
- once() — run it a single time8 tests · intermediate
DOM & eventsThe DOM is a live tree of objects — and JS can poke every branch of it.
7 min read2 exercises
2 exercises
- Build a mini event emitter10 tests · beginner
- Walk up to the nearest matching ancestor9 tests · beginner
Callbacks, then promisesHanding work to someone else, and getting the answer back later.
9 min read3 exercises
3 exercises
Errors & toolsThe last lesson before the beginner project — reading what the engine is trying to tell you.
6 min read2 exercises
2 exercises
- Parse JSON without crashing10 tests · beginner
- Throw a real, typed error9 tests · beginner
Guided project: build a to-do appEverything from the beginner chapters, in one small thing that works.
5 min read2 exercises
2 exercises
- Tick a to-do off, without mutating8 tests · beginner
- The filter bar and the items-left count8 tests · beginner
The cheat pageNot another lesson — the night-before-the-interview skim of the other 38.
6 min read

Practice34 exercises

Practice at this level

Every exercise opens in the editor with tests you can run.