The wiki today: 2 lessons · 16 concepts · 2 puzzles · 108 links between notes · 44 practice questions
A wiki that grows by one lesson a day. Each lesson teaches one idea properly, and every term in it links to its own note, so reading one page leads to the next. Hover over a link to preview it.
Today
#2 · Python's object model: what a Python variable really is, and why changing one list can change another. Today’s puzzle: Contains Duplicate.
Earlier: #1 · The event loop
Ways in
| If you want to | Go to |
|---|---|
| Learn something new today | The newest lesson, above (20-30 minutes) |
| Learn a topic from the ground up, in order | A path: How JavaScript runs your code |
| Look up a term quickly | The Glossary: every term in one line |
| Test yourself before an interview | Practice: every question in the wiki, answers hidden |
| Remember it for good | The Quiz: the same questions as flashcards, spaced so each comes back just before you’d forget it |
| Avoid the classic mistakes | Common traps: every gotcha in the wiki on one page |
| Know what employers want | What the job market asks for: this week’s most-requested skills, and what the wiki covers yet |
Every note says what to read first at the top, and what it leads to at the bottom, so you can always go one step back or one step forward.
How to read it
- Follow the links you don’t know yet. Hover for a preview; every note stands on its own.
- Answer the Check yourself questions before you open them. Testing yourself is what makes it stick; rereading doesn’t.
- Come back to Practice a few days later. Spacing the reviews out is the other half of remembering.
Tracks
| Track | What it covers |
|---|---|
| JavaScript | The event loop, closures, React, TypeScript, Node.js, web security |
| Python & Data | Python internals, SQL in depth, pandas, testing, pipelines |
| ML & Data Science | From linear regression to models in production |
| LLMs & RAG | Tokens, embeddings, retrieval, agents, evaluation |
| Backend & System Design | HTTP, APIs, caching, queues, scaling, consistency |
| CS Fundamentals | Complexity, memory, concurrency, networking, Git |
About
Written with Claude from primary sources (specs, RFCs, official docs), with code checked by running it. See about for how it is made and what it may get wrong.