Question

几行js代码的详细解释！

var Event_arr = hi_event.getElementsByTagName("a");
for (var i = 0; i < Event_arr.length; i++) {
Event_arr[i].style.top = (parseInt(Event_arr[i].style.top.replace('px', '')) - 1) + 'px';
if (parseInt(Event_arr[i].style.top.replace('px', '')) <= (0 - Event_height)) {
Event_arr[i].style.top = (Event_arr.length - 1) * Event_height + 'px';
var Event_height = Event_arr[0].clientHeight;

Answer 1

var Event_arr = hi_event.getElementsByTagName("a");\\得到所有标签为a的页面元素
for (var i = 0; i < Event_arr.length; i++) {\\循环遍历得到的元素
Event_arr[i].style.top = (parseInt(Event_arr[i].style.top.replace('px', '')) - 1) + 'px';\\元素向上移动一个像素
if (parseInt(Event_arr[i].style.top.replace('px', '')) <= (0 - Event_height)) {\\如果元素移出了边界，
Event_arr[i].style.top = (Event_arr.length - 1) * Event_height + 'px'; \\当前元素移到所有元素最下面

Answer 2

var Event_arr = hi_event.getElementsByTagName("a");
得到的是一个由对象组成的数组，对象都是<a></a><a></a>超链接标签

Event_arr[0] 这个数组里面第一个<a></a>

Answer 3

var Event_arr = hi_event.getElementsByTagName("a");//取出所有的a标签
for (var i = 0; i < Event_arr.length; i++) {
Event_arr[i].style.top = (parseInt(Event_arr[i].style.top.replace('px', '')) - 1) + 'px';//把a标签离父标签顶部像素-1
if (parseInt(Event_arr[i].style.top.replace('px', '')) <= (0 - Event_height)) {//判断离父标签顶部像素是否小于或等于离document高度
Event_arr[i].style.top = (Event_arr.length - 1) * Event_height + 'px'; //a标签总数*自已离document的高度给a标签离父标签顶部-像素

var Event_height = Event_arr[0].clientHeight;//取出离document的高度