Level 4: Data shaping · Exercise 57 of 76 · Free

Deep clone

A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.

The task

Return a deep copy of `value`, written by hand rather than with `structuredClone`. `value` is made of plain objects, arrays, Dates, strings, numbers (including `NaN`), booleans, `null` and `undefined`, nested to any depth, with no cycles. Every object, array and Date in the copy must be a new instance with the same contents, so changing the copy never changes the original. Primitives and `null` are returned as they are. Keys whose value is `undefined` are kept.

What this exercise teaches

Handling arrays, Dates and objects as separate cases is what keeps their types: a JSON round trip turns Dates into strings and drops undefined and NaN, and a spread copies only the top level, so nested objects are still shared with the original.

A hint if you get stuck

Recurse: `Array.isArray` for arrays (map over the items), `instanceof Date` for Dates (`new Date(value.getTime())`), `typeof value === "object"` for plain objects (copy each key), and return anything else unchanged.