实现select change 点击重复内容无法触发问题

var id = document.getElementById("addquerstions");id.onmousedown = function(){        this.sindex = this.selectedIndex;        this.selectedIndex = -1;    }    id.onmouseout = function() {        var index = id.selectedIndex;        if (index == -1) {            this.selectedIndex = this.sindex;        }    }