[jQuery]相对父级元素的fixed定位

(function($) {

    var DNG = {};

    //----------------------------------------------------/

    // 相对父级元素fixed

    //----------------------------------------------------/

    DNG.parentFixed = function() {

        // 获得需要fixed定位的元素

        var el =$(".parent-fixed");

        // 判断是否存在

        if( el.length > 0){

            el.each(function(){

                let $this = $(this);

                // 输入header为absolute或fixed定位的高度

                var headerFixed = 50 ;

                // 获得元素相关数据

                function getdata(ele){

                    // 获取父级元素 父级元素定位 父级元素高度

                    ele.parentOffset = ele.offsetParent();

                    ele.parentOffsetY = ele.parentOffset.offset().top - headerFixed;

                    ele.parentHeight = ele.parentOffset.height();

                    // 获取元素定位 元素高度

                    ele.oldPositionY = ele.positionY = ele.position().top;

                    ele.Height = ele.height();

                    // 计算元素滑动最大值 = 父级元素定位 + 父级元素高度 - 元素定位 - 元素高度

                    ele.maxScroll = ele.parentOffsetY + ele.parentHeight - ele.positionY - ele.Height;

                    return ele;

                }

                $this = getdata($this);

                // 窗口改变触发事件

                $(window).resize(function(){

                    // 更新元素相关数据

                    $this = getdata($this);

                });

                

                // 滑动触发事件

                $(window).scroll(function(){

                    $this.Scroll = $(window).scrollTop();

                    // 判断1：小于父级元素定位

                    // 判断2：大于父级元素定位,小于滑动最大范围

                    // 判断3：大于滑动最大范围

                    if( $this.Scroll < $this.parentOffsetY ){

                        $this.positionY = $this.oldPositionY;

                    } else if( $this.Scroll >= $this.parentOffsetY && $this.Scroll <= $this.maxScroll ){

                        // 计算元素Top定位,滑动距离 - 父级元素定位 + 元素定位

                        $this.positionY = $this.Scroll - $this.parentOffsetY + $this.oldPositionY;

                    } else{

                        $this.positionY = $this.maxScroll - $this.parentOffsetY + $this.oldPositionY;

                    }

                    // 改变元素定位

                    $this.css("top",$this.positionY);

                });

            });

        }

    };

    //----------------------------------------------------/

    // end

    //----------------------------------------------------/

    $(document).ready(function() {

        DNG.parentFixed();

    });

})(jQuery);