JS获取当前点击的子元素的下标

//子元素的class
var child = $(".child");
for (var i = 0; i < child.length; i++) {
    var a = child[i];
    a.index = i;//给每个className为child的元素添加index属性;
    a.onclick = function () {
        alert(this.index)
    }
}