Simple, standalone, vanilla implementation of lodash.cloneDeep

deepClone.js

// Simple implementation of lodash.cloneDeep
// Does not clone functions or handle recursive references.
export function deepClone(original) {
  if (original instanceof RegExp) {
    return new RegExp(original);
  } else if (original instanceof Date) {
    return new Date(original.getTime());
  } else if (Array.isArray(original)) {
    return original.map(deepClone);
  } else if (typeof original === 'object' && original !== null) {
    const clone = {};
    Object.keys(original).forEach(k => {
      clone[k] = deepClone(original[k]);
    });
    return clone;
  }
  return original;
}

deepClone.spec.js

import deepClone from './deepClone.js';

describe('deepClone', () => {
  it('creates a deep clone of an object', () => {
    const original = {
      foo: {
        a: 1,
        b: new Date()
      },
      bar: true,
      arr: ['a', 'b', { a: 9 }],
      b: null,
      c: undefined,
      d: 123,
      e: 234.56,
      f: 'asdfjkh',
      fn: () => { return true; },
      r: /[a-z]/i,
    };
    const clone = deepClone(original);
    expect(clone).toEqual(original);
    expect(clone.foo.b).not.toBe(original.foo.b);
    expect(clone.foo.b.getTime()).toBe(original.foo.b.getTime());
    expect(clone.arr).not.toBe(original.arr);
    expect(clone.arr).toEqual(original.arr);
    expect(clone.arr[2].a).toBe(original.arr[2].a);
    expect(clone.fn).toBe(original.fn);
    expect(clone.r).toEqual(original.r);
    expect(clone.r).not.toBe(original.r);
    expect(clone.fn()).toBe(original.fn());
  });

  it('makes a deep clone of an array', () => {
    const original = [1, 2, { a: 1, b: 2 }];
    let clone = deepClone(original);
    expect(clone).not.toBe(original);
    expect(clone).toEqual(original);
  });

  it('makes a clone of an object with object references', () => {
    const other = { a: 1, b: 2 };
    let original = {
      a: other,
      b: {
        a: other
      }
    };
    const clone = deepClone(original);
    expect(clone).toEqual(original);
    other.a = 3;
    expect(clone.a.a).toBe(1);
    expect(clone.b.a.a).toBe(1);
  });

  it('makes a clone of a string', () => {
    let original = 'hello';
    const clone = deepClone(original);
    expect(clone).toBe(original);
    expect(clone).toEqual(original);
    original = 'updated';
    expect(clone).not.toBe(original);
  });

  it('handles undefined', () => {
    const original = undefined;
    const clone = deepClone(original);
    expect(clone).toBe(original);
    expect(clone).toEqual(original);
  });

  it('handles null', () => {
    const original = null;
    const clone = deepClone(original);
    expect(clone).toBe(original);
    expect(clone).toEqual(original);
  });
});