沒有設置索引，屏幕上也能顯示呀？
<!DOCTYPE ?HTML>
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>數組</title>
<script type="text/javascript">
var arr=["*","##","***","&&","****","##"];
arr[7]="**" ;
alert(arr.length);
document.write(arr[3]);
?
我沒有設置arr[3]的索引，但是用document.wirte()屏幕上也能顯示&&
有什么影響嗎？？
2016-10-26
var arr=["*","##","***","&&","****","##"];定義數組時候已經有索引了