html select下拉菜单长度过长不出滚动条问题解决办法

<select class="form-control" data-edit-select="1" οnmοusedοwn="selectmousedown(this)"

οnblur="selectblur(this)" οnchange="selectchange(this)"

style="position:absolute;z-index:120">

</select>

function selectmousedown(ev) {if (ev.options.length > 5) {ev.size = 6;$(ev).css({"height": "auto","position": "absolute"})} else {$(ev).css("height", "28px")}}function selectblur(ev) {ev.size = 0;$(ev).css({"height": "28px","position": "static"})}function selectchange(ev) {ev.size = 0;$(ev).css({"height": "28px","position": "static"})}

结果如图：