1 <button onclick="Before()">前一天</button>
2 <button onclick="After()">后一天</button>
3 <div id="app"></div>

1 //获取时间戳
2 var Time = date.getTime();//当前的毫秒数
3 var oneDay = 1000*60*60*24;//一天的毫秒数

1 var date = new Date();
2 var app = document.getElementById("app");
3 app.innerHTML = myGetDate(date);

1 //封装日期格式化
2 function myGetDate(day){
3     return `${day.getFullYear()}年${day.getMonth()+1}月${day.getDate()}日`;
4 }

//计算前一天
function Before(){
    var before = Time - oneDay;//计算前一天的毫秒数
    date.setTime(before);
    app.innerHTML = myGetDate(date);
}

//计算后一天
function After(){
    var after = Time + oneDay;//计算后一天的毫秒数
    date.setTime(after);
    app.innerHTML = myGetDate(date);
}