Lesson 24 — Deep clone

Copy all the way down

A shallow copy ({ ...obj }) copies only the top level; inner objects are still shared, so changing copy.n.v also changes the original. A deep clone copies every level. Recursion makes it short: plain values are returned as they are; objects and arrays get a new container with each property deep-cloned.

typeof x !== "object" || x === null   // a plain value

Why it matters: hidden shared state is one of the hardest bugs to find.