初始值：

      var obj = {
        a: 1,
        b: 2,
        c: 3,
        d: 4,
        e: 5,
      };

第一种：for in

      for (let key in obj) {
        console.log(key + ":" + obj[key]);
      }

 第二种：Object.keys 获取key

      Object.keys(obj).forEach((key) => {
        console.log(key + ":" + obj[key]);
      });

 第三种：Object.keys 获取key  Object.values 获取value （第二种类似）

      for (let key in obj) {
        console.log(key + ":" + obj[key]);
      }

 第四种：Object.entries 搭配 for-of

      for (let [key, value] of Object.entries(obj)) {
        console.log(key + ":" + value);
      }

  第五种：Object.getOwnPropertyNames(obj) 返回数组

     Object.getOwnPropertyNames(obj).forEach((key) => {
        console.log(key + ":" + obj[key]);
      });

 第六种：Reflect.ownKeys(obj) 返回数组

      Reflect.ownKeys(obj).forEach((key) => {
        console.log(key + ":" + obj[key]);
      });