function UserInfo(info){
    this.username=info.username
    this.age=info.age
    // this.getInfo=(key)=>{
    //     return this[key]
    // }
    // this.setInfo=(key,value)=>{
    //     this[key]=value
    // }
}
UserInfo.prototype.getInfo=function(key){
    return this[key]
}
UserInfo.prototype.setInfo=function(key,value){
    this[key]=value
}

const userInfo=new UserInfo({
    username:"geyao",
    age:"18"
})


console.log(userInfo.getInfo('username'))
console.log(userInfo.getInfo('age'))

userInfo.setInfo('username',"fangfang")
userInfo.setInfo('age',19)
console.log(userInfo.getInfo('username'))
console.log(userInfo.getInfo('age'))

运行结果