js/25.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>
</head>
<body>
    <script>
        window.onload=function(){
            document.onwheel=function(event){
               // console.log(event  instanceof Event);
                //console.log(event  instanceof  WheelEvent);
                //console.log(event  instanceof  MouseEvent);
                //   wheelEvent对应的是继承来自MouseEvent，对应的MouseEvent对应的继承来自于Event的。
                console.log(event);
                if(event.wheelDelta<0){
                    console.log("滚轮向下滚动了");
                }else if(event.wheelDelta>0){
                    console.log("滚轮向上滚动了");
                }
            }
        }

        //  冒泡对应的是从下往上的操作的。
    </script>
</body>
</html>