JSintroes2022
structuredClone for deep copies
One call, a real deep copy.
Spreading an object copies only the top layer, so nested values stay shared and mutations leak back. structuredClone walks the whole graph for you — nested objects, Maps, Sets, Dates, even cycles — in a single built-in call, no JSON round-trip and its silent data loss.
The shallow-copy pitfall
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The spread leaks: writing shallow.nested.retries = 99 also shows 99 on the original because both share one nested object. After structuredClone, setting deep.nested.retries = 1 leaves the original at 99 — the nested level is genuinely its own copy.