| # | title | topic | type | difficulty |
|---|---|---|---|---|
| 1 | Flatten to any depth — no recursion allowed | Arrays | Coding | Medium |
| 2 | Build a matrix with Array.from | Arrays | Coding | Medium |
| 3 | One-pass tokenizer with flatMap | Arrays | Coding | Medium |
| 4 | Max of a nested structure — no loops | Math | Coding | Medium |
| 5 | Swap two values without a temp variable |
| Destructuring |
| Coding |
| Medium |
| 6 | Dissect a URL with new URL() | URL & Web APIs | Coding | Medium |
| 7 | Reverse an integer with do…while | Loops | Coding | Medium |
| 8 | Collatz stopping time with while | Loops | Coding | Medium |
| 9 | for…of with entries() and destructuring | Loops | Coding | Medium |
| 10 | Auto-vivifying counter (defaultdict) | Proxy & Reflect | Coding | Medium |
| 11 | The module pattern: private state via closure | YDKJS Book | Coding | Medium |
| 12 | once(fn) — run exactly one time | YDKJS Book | Coding | Medium |
| 13 | Insertion sort, in place | Sorting Algorithms | Coding | Medium |
| 14 | Tagged templates: redact the interpolations | YDKJS Book | Coding | Medium |
| 15 | Two Sum in one pass | Interview Classics | Coding | Medium |
| 16 | Balanced brackets with a stack | Interview Classics | Coding | Medium |
| 17 | Pair sum — approach 2: classic loops only | Arrays | Coding | Medium |
| 18 | Deep flatten — approach 2: recursion, no .flat() | Arrays | Coding | Medium |
| 19 | Deep max — approach 2: reduce(), Math.max banned | Math | Coding | Medium |
| 20 | Multiplication table — approach 2: nested for loops | Arrays | Coding | Medium |
| 21 | Weighted sum — approach 2: reduce(), no loops | Loops | Coding | Medium |
| 22 | Reverse an integer — approach 2: string methods | Loops | Coding | Medium |
| 23 | Collatz steps — approach 2: pure recursion | Loops | Coding | Medium |
| 24 | Tokenizer — approach 2: classic loops, no array methods | Arrays | Coding | Medium |
| 25 | Grid validation — approach 2: nested for loops | Arrays | Coding | Medium |
| 26 | Function composition — approach 2: a plain loop | Arrays | Coding | Medium |
| 27 | Depth-first search: recursive traversal | Algorithms & Recursion | Coding | Medium |
| 28 | Kill the O(n²) lookup | Patterns & Performance | Coding | Medium |
| 29 | Observer pattern with unsubscribe | Patterns & Performance | Coding | Medium |
| 30 | Prototype pattern: share the methods | Patterns & Performance | Coding | Medium |