| # | title | topic | type | difficulty |
|---|---|---|---|---|
| 91 | The lazy singleton pattern | Patterns & Performance | Coding | Hard |
| 92 | Observer pattern with unsubscribe | Patterns & Performance | Coding | Medium |
| 93 | Prototype pattern: share the methods | Patterns & Performance | Coding | Medium |
| 94 | Mixin pattern: compose behaviors | Patterns & Performance | Coding | Medium |
| 95 |
| Fix the loop capture |
| Scope & Hoisting |
| Coding |
| Medium |
| 96 | Build the DOM's listener brain | DOM Events | Coding | Hard |
| 97 | Build makeStub | Testing Lifecycle | Coding | Easy |
| 98 | Build makeSpy | Testing Lifecycle | Coding | Medium |
| 99 | Build the lifecycle harness itself | Testing Lifecycle | Coding | Hard |
| 100 | sleep(ms) — the promise every codebase re-invents | Async & Promises | Coding | Easy |
| 101 | Land three lines in three different queues | Async & Promises | Coding | Medium |
| 102 | Same results, a third of the wall clock | Async & Promises | Coding | Medium |
| 103 | A promise pool with a concurrency limit | Async & Promises | Coding | Hard |
| 104 | Retry with a delay between attempts | Async & Promises | Coding | Medium |
| 105 | A timeout wrapper that races | Async & Promises | Coding | Medium |
| 106 | Promisify an error-first callback API | Async & Promises | Coding | Medium |
| 107 | allSettled: report everything, fail at nothing | Async & Promises | Coding | Medium |
| 108 | First success wins — and AggregateError when none does | Async & Promises | Coding | Hard |
| 109 | A queue that keeps submission order | Async & Promises | Coding | Hard |
| 110 | forEach does not wait, and it will not tell you | Async & Promises | Coding | Medium |
| 111 | Debounce: only the last one survives | Async & Promises | Coding | Medium |
| 112 | Throttle: one call per window, no queue | Async & Promises | Coding | Medium |
| 113 | Cancel a timer that has not fired yet | Async & Promises | Coding | Hard |
| 114 | Batch every call made in the same tick | Async & Promises | Coding | Hard |
| 115 | Poll until it is ready, then stop | Async & Promises | Coding | Medium |
| 116 | The same sort, without writing a sort | Sorting Algorithms | Coding | Medium |
| 117 | The same check, in one pass of methods | Algorithms & Recursion | Coding | Medium |
| 118 | The same prefix, without shrinking a guess | Algorithms & Recursion | Coding | Medium |