鼠标滚动事件，鼠标滚动一下，屏幕滑动一屏

思路：1.判断鼠标向上还是向下滚动
2.执行鼠标事件
鼠标滚动事件注册事件资料：https://www.cnblogs.com/wsoft/articles/2856861.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">
    <script type="text/javascript" src='https://cdn.bootcss.com/jquery/3.4.1/jquery.min.js'></script>
    <script type="text/javascript" src='jquery-1.11.3.js'></script>
    <title>Document</title>
    <style>
        .a {
            height: 1000px;
            width: 80%;
            margin: 0 auto;
            background: #6498e1;
        }

        .a2 {
            height: 1000px;
            width: 80%;
            margin: 0 auto;
            background: #bb7878;
        }
    </style>
</head>

<body>
    <div class="a"></div>
    <div class="a2"></div>
    <div class="a"></div>
    <div class="a2"></div>
    <div class="a"></div>
    <div class="a2"></div>
    <script>
        var number = 0
        var gd = 0
        //  向下滚动还是向下滚动
        var scrollFunc = function (e) {
            gd = e.wheelDelta;
        }
        if (document.addEventListener) {
            document.addEventListener('DOMMouseScroll', scrollFunc, false);
        } //W3C  
        window.onmousewheel = document.onmousewheel = scrollFunc; //IE/Opera/Chrome/Safari  
        // scrop距离
        var isScrolling = false //是否在滚动
        listenAndScroll()

        // 无限滚动
        function listenAndScroll() {
            $(document).scroll(function () {//执行几千次
                var b = $(window).scrollTop();
                if (isScrolling) {
                    return
                }//如果isScrolling为true就跳出去
                isScrolling = true//
                var scrollGap = 1000
                if (b > 0 && gd < 0) {
                    let isBlock = b % scrollGap === 0 //%取余 余为零
                    console.log(isBlock, b % scrollGap, b)
                    if (isBlock) {
                        return isScrolling = false//如果isBlock为true就跳出并isScrolling = false
                        //跳出之后终止语句
                    }
                    let pos = (Math.floor(b / scrollGap) + 1) * scrollGap
                    console.log(pos)
                    $("html").animate({
                        scrollTop: pos
                    }, "slowly", function () {
                        isScrolling = false;
                    });

                }
                else if (b > 0 && gd > 0) {
                    let isBlock2 = b % scrollGap === 0
                    // console.log(b,isBlock2,scrollGap)
                    if (isBlock2) return isScrolling = false
                    let pos2 = (Math.ceil(b / scrollGap) - 1) * scrollGap
                    console.log(pos2)
                    $("html").animate({
                        scrollTop: pos2
                    }, "slowly", function () {
                        isScrolling = false
                    });
                }
                else {
                    isScrolling = false
                }
            })
        }

    </script>
</body>

</html>