BOM：Browser Object Model

计时器

计时器是异步的，当时机成熟之后才会执行

计时器会返回一个数字，该数字表示计时器的编号

setTimeout方法：指定时间到达后运行某个函数
- clearTimeout方法：清除计时器
setInterval方法：指定间隔时间到达后运行某个函数
- clearInterval方法：清除计时器

   // 
    timer1 = setTimeout(function() {
        console.log("延迟计时器1");
    }, 3000);

    clearTimeout(timer1);

    // 
    timer2 = setInterval(function() {
        console.log("间歇计时器2");
    });

    clearInterval(timer2);

练习

文字时钟

html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body {
            text-align: center;
        }
    </style>
</head>
<body>
    <h1></h1>
    <script>
        var h1 = document.querySelector("h1");

        function setTime() {
            var date = new Date();
            var hour = date.getHours();
            var minute = date.getMinutes();
            var second = date.getSeconds();
            h1.innerHTML = `${hour.toString().padStart(2,"0")}:${minute.toString().padStart(2,"0")}:${second.toString().padStart(2,"0")}`;
        }

        setTime();
        setInterval(setTime, 1000);
    </script>
</body>
</html>

APM计时器

html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body {
            text-align: center;
        }

        p {
            font-size: 2em;
        }
    </style>
</head>

<body>
    <p>
        倒计时：<span id="spanclock">5</span>
    </p>
    <p>
        点击数：<span id="spannum">0</span>
    </p>
    <p>
        <button id="btnadd">点击</button>
        <button id="btnreset">重置</button>
    </p>
    <script>
        var num = 0,
            clock = 5, //倒计时
            timer, //计时器id
            isOver = false, //是否结束
            spanNum = document.getElementById("spannum"),
            btnAdd = document.getElementById("btnadd"),
            btnReset = document.getElementById("btnreset"),
            spanClock = document.getElementById("spanclock");

        btnAdd.onclick = function () {
            if (num === 0) {
                setClock();
            }
            if (!isOver) {
                setNum(num + 1);
            }
        }

        btnReset.onclick = function () {
            setNum(0);
            clock = 5;
            spanClock.innerText = clock;
            isOver = false;
        }

        function setNum(n) {
            num = n;
            spanNum.innerText = num;
        }

        //开启一个倒计时
        function setClock() {
            if (timer) {
                return;
            }
            timer = setInterval(function () {
                clock--;
                spanClock.innerText = clock;
                if (clock === 0) {
                    clearInterval(timer);
                    timer = null;
                    isOver = true; //结束了
                }
            }, 1000);
        }
    </script>
</body>

</html>

触碰反弹小球

html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .move {
            position: fixed;
            left: 0;
            top: 0;
            width: 100px;
            height: 100px;
            border-radius: 50%;
            background: red;
        }
    </style>
</head>

<body>
    <div class="move">
        <!-- 该div自动向右下移动，遇到边界反弹 -->
    </div>
    <script>
        var div = document.querySelector(".move"),
            x = 0, //初始坐标x
            y = 0, //初始坐标y
            xDis = 2, //每次移动x的距离
            yDis = 2, //每次移动y的距离
            duration = 16, //移动的间隔时间
            width = 100,
            height = 100;

        setInterval(function() {
            x += xDis;
            y += yDis;
            //边界判定
            if (y >= document.documentElement.clientHeight - height) {
                y = document.documentElement.clientHeight - height;
                yDis = -yDis;
            }
            if (y <= 0) {
                y = 0;
                yDis = -yDis;
            }

            if (x <= 0) {
                x = 0;
                xDis = -xDis;
            }
            if (x >= document.documentElement.clientWidth - width) {
                x = document.documentElement.clientWidth - width;
                xDis = -xDis;
            }

            div.style.left = x + "px";
            div.style.top = y + "px";
        }, duration);
    </script>
</body>

</html>

计时器 ​

练习 ​

计时器

练习