js中如何往对象中添加属性

let obj = {'a':123};

let obj1 = {'c':1,'d':2};

let twoobj = Object.assign(obj1,obj);
//两个注意的点：
//用一个新的名称来接受Object.assign的值；不要用obj1来接受，会报错
//第一个参数是原来的对象，第二个是要添加进去的对象；

this.videoList = []
      const data = await this.$http.post('Course/shows', {
        type: nedCuriculums.type,
        grade: nedCuriculums.grade,
        classtype: nedCuriculums.classtype,
        subject: nedCuriculums.subject,
        term: term
      }).catch(err => err)
      this.term = term
      var videoList = data.data
-----------------------------------------------------------
// 假如数据是这样：
videoList = [
	{
		id: 1
		type: "同步课程",
        grade: "一年级",
        classtype: "xxx",
        subject: "数学",
        term: "上"
     }，
     {
     	id: 2
		type: "同步课程",
        grade: "一年级",
        classtype: "xxx",
        subject: "数学",
        term: "上"
     }
]

// 第一种方法，给对象动态添加属性 for of  根据对象
 var newvideoList = {}
 for (var item of videoList) {
   newvideoList = {
     isHover: false,
     dirname: item.dirname,
     id: item.id,
     resourceId: item.resourceId
   }
   this.videoList.push(newvideoList)
 }	

// 第2种方法  for in  根据下标
  for (var index in videoList) {
    videoList[index].isHover = false
    this.videoList.push(videoList[index])
    console.log(index)
    this.videoList.push(videoList[index])
  }