One JavaScript Interview Question, Two Correct Answers — Tested

Original tested JavaScript interview and code-review lesson: first repeat encountered versus earliest original position, Set invariant, boundary tests, nonmutation and operation counts. Original code cards and diagrams; not a native VS Code recording. Cedar AI-generated narration. Node22.19.0. Source: https://developer.mozilla.org/en-US/docs/W... Code examples: https://github.com/ShortcutProof/shortcut-... Free practice: https://payhip.com/b/Ph0TY #JavaScript #CodingInterview #CodeReview Chapters: 00:00 One question. Two answers. 00:52 Write the contract first. 01:40 A plausible answer can be wrong. 02:31 Check before adding. 03:22 Boundary tests protect the interface. 04:15 Sorting changes the question. 05:10 Count work before timing it. 06:12 Review the whole promise. Full scene programs: https://github.com/ShortcutProof/shortcut-... The string-ID contract is a precondition; the core helper does not itself validate input types. Set time complexity is stated under common hash-implementation assumptions, not universally guaranteed. Narration slowed to86% for readable code pacing.