let math = {    subject: '数学',    children: [        { id: 1, title: '数一' },         { id: 2, title: '数二' },         { id: 3, title: '数三' },         { id: 0, title: '待定' }    ]}// 增加新属性math.remark = "备注";// 删除对象中某一属性delete math.subject

后果：