道理

1.猎取当前对象及当前对象的一切对象的高度和，猎取当前父盒子的高度
2.运用jquery的animate动画处置惩罚

css款式

*{margin:0;padding:0;}
.parent{list-style-type:none;height:300px;width:120px;overflow-y:scroll;}
.child{height:38px;border-top:2px solid red;background: green;line-height: 38px;}

html代码段

<ul class="parent">
    <li class="child">阿里巴巴</li>
    <li class="child">腾讯</li>
    <li class="child">百度</li>
    <li class="child">华为</li>
    <li class="child">遐想</li>
    <li class="child">万科</li>
    <li class="child">万达</li>
    <li class="child">恒大</li>
    <li class="child">小米</li>
    <li class="child">京东</li>
    <li class="child">格力</li>
    <li class="child">美的</li>
    <li class="child">海尔</li>
</ul>

javascript代码段

var 
parentNode = $( '.parent' ),
childHeight = 40,
parentNodeHeight = 300;
$('.child').click(function(){
    var j = $(this).index();
    parentNode.stop().animate({
        scrollTop : childHeight * ( j + 1 ) - parentNodeHeight / 2 // 中心代码
    },600);
});

url参数猎取

const getUrlParam = function ( mid, hashOn=false ) {
  const reg = new RegExp("(^|&)" + mid + "=([^&]*)(&|$)");
  const util = idx => window.location[ idx ].substr(1).match(reg);
  const r = util('search') || ( hashOn && util( 'hash' ) ) || null;
  if ( r != null )  
    return decodeURIComponent( r[2] ); 
  return null;
}