this.$set的使用方法

//对象的属性sex的值更新为"男"
let obj = {name:"六四",age:18,sex:"女"}

this.$set(obj,"sex","男")   //第一个参数是对象，第二个参数是更新的属性名称，第三个参数是新的内容

//更新之后的obj是 {name:"六四",age:18,sex:"男"}

let arr = ["星期一","星期二","星期日"]
this.$set(arr,2,"星期三")   //第一个参数是数组，第二个参数是下标索引，第三个参数是新的内容
//更新之后的arr是["星期一","星期二","星期三"]