深拷贝

function deepClone(target,map = new WeakMap) {
  if(typeof target !== 'object' | typeof target == null) return target 
  if(map.has(target)) return map.get(target)
 
  const clonedTarget  = Array.isArray(target) ? [] : {}
  map.set(target,clonedTarget) //先占位，后续在遍历的时候会直接通过索引填值 
  
  for (const key in target) {
    if (target.hasOwnProperty(key)) {
      // 递归调用
      clonedTarget[key] = deepClone(target[key],map)
    }
  }
  return clonedTarget 
}