JavaScript fundamentals for engineers
By the end of today you can read JavaScript confidently by mapping it onto what you already know from Python, and you can name the handful of genuine differences that cause real bugs.
YesterdayEverything since Day 1 was taught in Python, deliberately. Today proves those concepts were never about Python.
TomorrowTomorrow you meet the one part of JavaScript with no Python equivalent: the event loop.
Why this matters
You do not need to love JavaScript, but every frontend, most tooling, and a large share of the code an AI writes for you is in it. Reading it fluently is not optional.
- JavaScript
- Where instincts mislead
- Closures
- this and arrow functions
Learn it
75 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
5 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
45 minTake any Python script you wrote in Phase 1, ideally one with a function, a loop and a dictionary, and rewrite it in JavaScript so it produces identical output when run with node. Then write down every place the translation was not one to one.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01The concepts transferred; only the syntax and a few traps changed
- 02const prevents rebinding, not mutation
- 03Use === always; == converts types before comparing
- 04An empty array is truthy in JavaScript and falsy in Python
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.