JS日期联动及时间差计算

题目：

要求：在页面中显示当前日期，输入的日期、并显示两个日期相差天数、以及这两个日期分别是星期几
结果展示：

项目代码：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>测试</title>
</head>
<!-- 在页面中显示当前日期，输入的日期、并显示两个日期相差天数、以及这两个日期分别是星期几 -->
<body onload="load()">
<input type="text" id="time" style=" 300px;height: 45px;font-size: 18px;text-align: center;"><br><br>
<form name="selectDate" action="">
<select onchange="updateDay(selectDate.yyyy.value,selectDate.mm.value),getWeek(selectDate.yyyy.value,selectDate.mm.value,selectDate.dd.value)" name="yyyy" id="yyyy" style=" 80px;height: 30px;font-size: 18px;text-align: center;"></select>年
<select onchange="updateDay(selectDate.yyyy.value,selectDate.mm.value),getWeek(selectDate.yyyy.value,selectDate.mm.value,selectDate.dd.value)" name="mm" id="mm" style=" 80px;height: 30px;font-size: 18px;text-align: center;"></select>月
<select onchange="getWeek(selectDate.yyyy.value,selectDate.mm.value,selectDate.dd.value)" name="dd" id="dd" style=" 80px;height: 30px;font-size: 18px;text-align: center;"></select>日
<span id="week"></span>
</form>
<hr>
<button onclick="clas()">计算时间差</button>
<input type="text" readonly="readonly" id="dateDiff">
</body>
<script>
var time = document.getElementById('time');
var newWeek = document.getElementById("week");
var dateDiff = document.getElementById("dateDiff");
function fun(){    
    var now = new Date();
    var year = now.getFullYear();
    var month = now.getMonth()+1;
    var day = now.getDate();
    var hours = now.getHours();
    var min = now.getMinutes();
    var sec = now.getSeconds();
    var week = now.getDay();
    time.value = year+"年"+month+"月"+day+"日  "+hours+":"+min+":"+sec+"  星期"+a[week];
}
var a = ["日","一","二","三","四","五","六"];
//定时任务
setInterval(function(){
    fun();
},1000)

//自定义日期
function setDate(yyyy,mm){
    var sDate = new Date(yyyy,mm,0);
    console.log(sDate)
    return sDate;
}

var mList = [1,3,5,7,8,10,12];
//根据年月更新日期
function updateDay(yyyy,mm){
    var date = new Date();
    newDate = setDate(yyyy,mm);
    while(document.all.dd.childNodes.length>0){
        document.all.dd.removeChild(document.all.dd.childNodes[0]);
    }
    for (var i = 1; i <= newDate.getDate(); i++) {
        option = document.createElement("option");
        option.value = i;
        option.appendChild(document.createTextNode(i));
        document.all.dd.appendChild(option);
        if (date.getDate() == i) {
            option.selected = true;
        }
    }
}

//初始化工作
function load(){
    //初始化年
    var date = new Date();
    var year = date.getFullYear();
    var y = 0;
    var m = 0;
    for (var i = year-10; i < year+15; i++) {
        option = document.createElement("option");
        option.value = i;
        option.appendChild(document.createTextNode(i));
        document.all.yyyy.appendChild(option);
        if (i == year) {
            option.selected = true;
            y = i;
        }
    }
    //初始化月
    for (var i = 1; i <= 12; i++) {
        option = document.createElement("option");
        option.value = i;
        option.appendChild(document.createTextNode(i));
        document.all.mm.appendChild(option);
        if (i == date.getMonth()+1) {
            option.selected = true;
            m = i;
        }
    }
    //初始化月
    var dd = ymChange(y,m);
    for (var i = 1; i <= dd; i++) {
        option = document.createElement("option");
        option.value = i;
        option.appendChild(document.createTextNode(i));
        document.all.dd.appendChild(option);
        if (date.getDate() == i) {
            option.selected = true;
        }
    }
    //显示星期几
    newWeek.innerText = "   星期"+a[date.getDay()];
}

//判断平年闰年
function isRunYear(yyyy){
    return ((yyyy%4==0&&yyyy%100!=0)||(yyyy%400==0));
}

//年和月发生变化
function ymChange(yyyy,mm){
    if (isRunYear(yyyy)) {
        if (mm == 2) {
            return 29;
        }else if(mList.indexOf(mm) >= 0){
            return 31;
        }else{
            return 30;
        }
    }
    if (!isRunYear(yyyy)) {
        if (mm == 2) {
            return 28;
        }else if(mList.indexOf(mm) >= 0){
            return 31;
        }else{
            return 30;
        }
    }
}

//判断星期几
function getWeek(yyyy,mm,dd){
    var newDate = new Date(yyyy,mm-1,dd);
    newWeek.innerText = "   星期"+a[newDate.getDay()];
}

//计算时间差
function clas(){
    var yyyy = document.getElementById('yyyy').value;
    var mm = document.getElementById("mm").value;
    var dd = document.getElementById("dd").value;
    var nDate = new Date();
    var sDate = new Date(yyyy,mm-1,dd);
    var daysDiff = (sDate.getTime() - nDate.getTime())/(1000*60*60*24);
    dateDiff.value = Math.abs(Math.ceil(daysDiff));
}
</script>
</html>