开关灯效果

代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        img{
            display:inline-block;
            width:170px;
            height:270px;
        }
    </style>
</head>
<body>
    <img src="images/bright.jpg" alt="">

    <script>
        var img = document.getElementsByTagName('img')[0];

        // 自定义 属性
        var flag = true;   // 假设 开关flag 值  true-亮   false-灭
        img.onclick = function(){
            if(flag){  // flag是否为true  是不是亮的
                img.src = 'images/dark.jpg';
                flag = false;
            }else{
                img.src = 'images/bright.jpg';
                flag = true;
            }

        }
    </script>
</body>
</html>