js内置对象

news2024/9/21 22:37:17

包装类

<script>
    /*var a=new Number(123);
    var b=new String("慕课网");
    var c=new Boolean(true);*/
    var a = 123;
    var b = '慕课网';
    var c = true;
    console.log(a);
    console.log(typeof a);
    console.log(b);
    console.log(typeof b);
    console.log(c);
    console.log(typeof c);
</script>

    var a=new Number(123);
    var b=new String("慕课网");
    var c=new Boolean(true);
    /*var a = 123;
    var b = '慕课网';
    var c = true;*/
    console.log(a);
    console.log(typeof a);
    console.log(b);
    console.log(typeof b);
    console.log(c);
    console.log(typeof c);

    var d=456;
    console.log(d.__proto__===Number.prototype);

包装类知识总结

Math对象

Math.round()方法：四舍五入

Math.max()方法：如何求数组最大值

Math.random()方法：获取[0,1)区间随机数

生成[a,b]之内的整数：eg:[3,8] parseInt(Math.random()*6)+3

Date日期对象

字符串的话创建日期对象，它会算时区，8点（第三个创建形式）

时间戳

倒计时小案例

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>倒计时</title>
</head>
<body>
<h1>2023年高考倒计时</h1>
<h2 id="info"></h2>
<script>
    var info=document.getElementById('info');
    setInterval(function (){
        var nd = new Date();
        var td = new Date(2023, 5, 7);
        // 毫秒差
        var diff = td - nd;
        //把diff换算为天，小时，分，秒
        var day = parseInt(diff / (1000 * 60 * 60 * 24));
        var hour = parseInt(diff % (1000 * 60 * 60 * 24) / (1000 * 60 * 60));
        var minute = parseInt(diff % (1000 * 60 * 60) / (1000 * 60));
        var second = parseInt(diff % (1000 * 60 * 60) % (1000 * 60) / 1000);

        info.innerText=day+'天'+hour+'时'+minute+'分'+second+'秒';
    },1000);
</script>
</body>
</html>