implement object deep clone

JavaScript deepClone.js

function deepClone(source, hash = new WeakMap()) {
  if (source === null || typeof source !== 'object') {
    return source;
  }
  if (source instanceof Date) {
    return new Date(source);
  }
  if (source instanceof RegExp) {
    return new RegExp(source);
  }
  
  if (hash.has(source)) {
    return hash.get(source);
  }
  
  const ins = new source.constructor();
  hash.set(source, ins);
  for (const key in source) {
    if (source.hasOwnProperty(key)) {
      ins[key] = deepClone(source[key], hash);
    }
  }

  return ins;
}