箭头函数的应用3-13编程练习作业提交

来源：3-13 编程练习

慕越秀工地

2022-07-19 00:16:36

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Document</title>
    <style>
        div {
            width: 300px;
            margin: 20px 0;
            line-height: 30px;
            background: yellowgreen;
        }
    </style>
</head>
<body>
    <button id="start">开始</button>
    <button id="stop">停止</button>
    <div id="box"></div>
    <script>
        const startBtn = document.getElementById('start')
        const stopBtn = document.getElementById('stop')
        const box = document.getElementById('box')
        var show = {
            content: "Hello World",
            timer: null,
            start: function () {
                // 在此补充代码
                startBtn.addEventListener(
                    'click',
                     () => {
                        setInterval(() => {
                            console.log(this);
                            show.timer += show.content;
                            box.innerHTML = show.timer;
                        },1000);
                     },
                     false
                     );
            },
            stop: function () {
                // 在此补充代码
                stopBtn.addEventListener(
                    'click',
                     ()=> {
                        clearInterval();
                })
            },
        }
         // 在此补充代码
         show.start();
         show.stop();
    </script>
</body>
</html>

老师，这题我的代码为啥实现效果的时候多了个null