| # | title | topic | type | difficulty |
|---|---|---|---|---|
| 31 | Collatz stopping time with while | Loops | Coding | Medium |
| 32 | for…of with entries() and destructuring | Loops | Coding | Medium |
| 33 | unknown vs any | TypeScript | Multiple choice | Medium |
| 34 | Write the narrowing a compiler would demand | TypeScript | Coding | Hard |
| 35 | IEEE 754 quirks | Floating Point |
| Multiple choice |
| Hard |
| 36 | Sum prices to the exact cent | Floating Point | Coding | Hard |
| 37 | Split a payment — never lose a cent | Payments | Coding | Hard |
| 38 | Reconcile a payment ledger | Payments | Coding | Hard |
| 39 | The get trap intercepts everything | Proxy & Reflect | Multiple choice | Medium |
| 40 | has trap + Reflect + invariants | Proxy & Reflect | Multiple choice | Hard |
| 41 | Python-style negative array indexes | Proxy & Reflect | Coding | Hard |
| 42 | Type-enforcing object via set trap | Proxy & Reflect | Coding | Hard |
| 43 | Auto-vivifying counter (defaultdict) | Proxy & Reflect | Coding | Medium |
| 44 | What 'use strict' actually changes | Strict Mode | Multiple choice | Hard |
| 45 | Make a plain object for…of-able | Loops | Coding | Hard |
| 46 | The four this-binding rules, in precedence order | YDKJS Book | Multiple choice | Hard |
| 47 | Build bind() yourself (hard binding) | YDKJS Book | Coding | Hard |
| 48 | typeof's famous lies | YDKJS Book | Multiple choice | Medium |
| 49 | The module pattern: private state via closure | YDKJS Book | Coding | Medium |
| 50 | Automatic Semicolon Insertion strikes | YDKJS Book | Multiple choice | Medium |
| 51 | once(fn) — run exactly one time | YDKJS Book | Coding | Medium |
| 52 | Rebuild Array.prototype.reduce — holes and all | Arrays | Coding | Hard |
| 53 | Rebuild Array.prototype.with (ES2023) | Arrays | Coding | Hard |
| 54 | take(iterable, n) — lazy, infinite-safe | Loops | Coding | Hard |
| 55 | curry(fn) — collect arguments until arity is met | YDKJS Book | Coding | Hard |
| 56 | Reimplement == from the spec (without using ==) | Type Coercion | Coding | Hard |
| 57 | Rebuild Object.groupBy — null prototype included | Objects | Coding | Hard |
| 58 | deepEqual that survives circular references | Objects | Coding | Hard |
| 59 | memoize(fn) — cache by identity, even undefined | YDKJS Book | Coding | Hard |
| 60 | b + a + + a + a | WTF Quirks | Multiple choice | Medium |