為什么把<script>的代碼都放在<head>里就沒(méi)有效果了呢
<script type="text/javascript">
window.onload=function(){
var area = document.getElementById('moocBox');
?var con1 = document.getElementById('con1');
?var con2 = document.getElementById('con2');
?var speed = 50;
?area.scrollTop = 0;
?con2.innerHTML = con1.innerHTML;
?function scrollUp(){
?? ? if(area.scrollTop >= con1.scrollHeight) {
?? ??? ? area.scrollTop = 0;
?? ??? ? }else{
?? ??? ??? area.scrollTop ++;
?? ??? ? }
}
var myScroll = setInterval("scrollUp()",speed);
area.onmouseover = function(){
?? ? clearInterval(myScroll);
?? ?}
area.onmouseout = function(){
?? ? myScroll = setInterval("scrollUp()",speed);
?? ?}
}
?</script>
2016-03-04
網(wǎng)頁(yè)加載是有順序的！有的需要先加載DOM在加載JS!
我認(rèn)為將JS放到head里，瀏覽器會(huì)首先加載JS而后再加載html文檔里的其他內(nèi)容，所以若js中用到了后面的DOM結(jié)構(gòu)等，而后面的DOM結(jié)構(gòu)等都沒(méi)有加載完畢，就會(huì)出現(xiàn)這種情況，