JavaScript shallow clone

shallow-clone.js

/**
 * Creates a shallow copy of an Object or an Array, such that, 
 * `a !== shallowClone(a)`, but `a.b === shallowClone(a).b`, where `b` 
 * is not a primitive value. Deep cloning is out of scope here.
 * 
 * @param {*} item - any “simple” `Object` or `Array`
 * @return {*}
 * @throws {TypeError} - if an Object does not directly inherit from 
 *                       `Object.prototype` or `null`
 */
function shallowClone(item) {
  if ('object' !== typeof item) return item;

  if (Array.isArray(item)) return [...item];

  const isSimpleObject = x =>
    [null, Object.prototype].some(type => type === Object.getPrototypeOf(x));
  if (!isSimpleObject(item)) {
    throw new TypeError();
  }

  return Object.assign(Object.create(null), item);
}