实现一个深克隆（考虑环）

[ScoutYin]

const deepClone = (parent) => {
   const parents = [], children = []
   const _clone = (parent) => {
     if (parent === null) return null
     if (typeof parent !== 'object' && typeof parent !== 'function') return parent
     let child
     child = Object.prototype.toString.call(parent) === '[object Array]' ? [] : {}
     const index = parents.indexOf(parent)
     if (index !== -1) {
	return children[index]
     }
     parents.push(parent)
     children.push(child)
     Object.keys(parent).forEach((key) => {
	child[key] = typeof parent[key] === 'object' ? _clone(parent[key]) : parent[key]
     })
     return child
     }
  return _clone(parent)
}

test

const obj = {
    a: 1,
    b: {
        c: [
	      {
		   d: 2
	      }
	   ]
	}
}
obj.b.c[0].d = obj.b
const newObj = deepClone(obj)
newObj.b.f = 3
console.log(obj, newObj)