deepClone

Creates a deep clone of an object. Clones primitives, arrays and objects, excluding class instances.

• Use recursion.
• Check if the passed object is null and, if so, return null.
• Use Object.assign() and an empty object ({}) to create a shallow clone of the original.
• Use Object.keys() and Array.prototype.forEach() to determine which key-value pairs need to be deep cloned.
• If the object is an Array, set the clone's length to that of the original and use Array.from(clone) to create a clone.

const deepClone = obj => {
  if (obj === null) return null;
  let clone = Object.assign({}, obj);
  Object.keys(clone).forEach(
    key =>
      (clone[key] =
        typeof obj[key] === 'object' ? deepClone(obj[key]) : obj[key])
  );
  if (Array.isArray(obj)) {
    clone.length = obj.length;
    return Array.from(clone);
  }
  return clone;
};

const a = { foo: 'bar', obj: { a: 1, b: 2 } };
const b = deepClone(a); // a !== b, a.obj !== b.obj