| # | title | topic | type | difficulty |
|---|---|---|---|---|
| 1 | Array.prototype.at is generic | Arrays | Multiple choice | Hard |
| 2 | Pair sum detection with .some() only | Arrays | Coding | Hard |
| 3 | Matrix validation with .every() | Arrays | Coding | Hard |
| 4 | Function composition with reduceRight | Arrays | Coding | Hard |
| 5 | Sparse arrays and holes |
| Arrays |
| Multiple choice |
| Hard |
| 6 | The + operator: string context wins | Type Coercion | Multiple choice | Hard |
| 7 | The == algorithm, step by step | Type Coercion | Multiple choice | Hard |
| 8 | Take control of ToPrimitive | Type Coercion | Coding | Hard |
| 9 | Microtasks vs macrotasks | Quiz: JS Questions | Drag & drop | Hard |
| 10 | Group transactions by risk bucket | Objects | Coding | Hard |
| 11 | What Object.groupBy actually returns | Objects | Multiple choice | Hard |
| 12 | Relative URL resolution | URL & Web APIs | Multiple choice | Hard |
| 13 | Which sink executes? | Security | Multiple choice | Hard |
| 14 | Labeled break out of nested loops | Loops | Coding | Hard |
| 15 | Write the narrowing a compiler would demand | TypeScript | Coding | Hard |
| 16 | IEEE 754 quirks | Floating Point | Multiple choice | Hard |
| 17 | Sum prices to the exact cent | Floating Point | Coding | Hard |
| 18 | Split a payment — never lose a cent | Payments | Coding | Hard |
| 19 | Reconcile a payment ledger | Payments | Coding | Hard |
| 20 | has trap + Reflect + invariants | Proxy & Reflect | Multiple choice | Hard |
| 21 | Python-style negative array indexes | Proxy & Reflect | Coding | Hard |
| 22 | Type-enforcing object via set trap | Proxy & Reflect | Coding | Hard |
| 23 | What 'use strict' actually changes | Strict Mode | Multiple choice | Hard |
| 24 | Make a plain object for…of-able | Loops | Coding | Hard |
| 25 | The four this-binding rules, in precedence order | YDKJS Book | Multiple choice | Hard |
| 26 | Build bind() yourself (hard binding) | YDKJS Book | Coding | Hard |
| 27 | Rebuild Array.prototype.reduce — holes and all | Arrays | Coding | Hard |
| 28 | Rebuild Array.prototype.with (ES2023) | Arrays | Coding | Hard |
| 29 | take(iterable, n) — lazy, infinite-safe | Loops | Coding | Hard |
| 30 | curry(fn) — collect arguments until arity is met | YDKJS Book | Coding | Hard |