深度拷贝

const isObject = function(obj) {
  if (obj === null || obj === undefined) return false;
  if (typeof obj === "object") return true;
};

const isArray = function(arr) {
  return Array.isArray(arr);
};

const deepClone = function(obj) {
  if (!isObject(obj)) return obj;
  let cloneObj = isArray(obj) ? [] : {};
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      let value = obj[key];
      if (isObject(value)) {
        cloneObj[key] = deepClone(value);
      } else {
        cloneObj[key] = value;
      }
    }
  }
  return cloneObj;
};

分别对extend 和 clone 库进行了性能测试比对... 发现extend 贼牛逼

源码分析 : extend