<script language="javascript">
var mynum=new Array(65,90,88,98);
var mynum[12]=87;
document.write("数组的长度是:"+ mynum.length );
</script>
var mynum[12]=87; var要去掉吧 又声明个变量?
<script language="javascript">
var mynum=new Array(65,90,88,98);
mynum[12]=87;
document.write("数组的长度是:"+ mynum.length );
</script>
楼上说得对!