← All tasksJavaScript · Senior

deepClone: deep copy

Write a function deepClone(value) that makes a deep copy of objects, arrays, Date, Map and Set at any depth. Primitives and functions are returned as is.

The copy must survive circular references (obj.self = obj) and preserve shared references: if two fields pointed to one object, in the copy they point to one copy too. Solve it without structuredClone.

function deepClone(value) {
  // ...
}

Ctrl+Enter runs the tests. Tab indents; to leave the editor with the keyboard, press Esc and then Tab. Your code is saved in this browser.

Tests (7)

const src = { a: 1, nested: { b: [1, { c: 2 }] } };
const copy = deepClone(src);
expect(copy).toEqual(src);
expect(copy.nested === src.nested).toBe(false);
expect(copy.nested.b[1] === src.nested.b[1]).toBe(false);

const date = new Date('2024-01-02T03:04:05Z');
const copy = deepClone({ date });
expect(copy.date).toBeInstanceOf(Date);
expect(copy.date.getTime()).toBe(date.getTime());
expect(copy.date === date).toBe(false);

const src = { m: new Map([['k', { v: 1 }]]), s: new Set([1, 2]) };
const copy = deepClone(src);
expect(copy).toEqual(src);
expect(copy.m.get('k') === src.m.get('k')).toBe(false);
expect(copy.s === src.s).toBe(false);

const src = { name: 'root' };
src.self = src;
const copy = deepClone(src);
expect(copy.self).toBe(copy);
expect(copy === src).toBe(false);

const shared = { x: 1 };
const copy = deepClone({ a: shared, b: shared });
expect(copy.a).toBe(copy.b);
expect(copy.a === shared).toBe(false);

expect(deepClone(5)).toBe(5);
expect(deepClone(null)).toBe(null);
expect(deepClone('x')).toBe('x');

const f = () => 1;
expect(deepClone({ f }).f).toBe(f);