为什么第二种输出就是undefined
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>二维数组</title>
<script type="text/javascript">
var myarr = new Array();
//1
for(var i=0;i<3;i++){
myarr[i] = new Array();
for(var j=0;j<6;j++){
myarr[i][j]=i*j;
document.write(myarr[i][j]);
}
document.write("<br />");
}
//2
for(var i=0;i<3;i++){
myarr[i] = new Array();
for(var j=0;j<6;j++){
document.write(myarr[i][j]);
}
document.write("<br />");
}
</script>
</head>
<body>
</body>
</html>结果
000000
012345
0246810
undefinedundefinedundefinedundefinedundefinedundefined
undefinedundefinedundefinedundefinedundefinedundefined
undefinedundefinedundefinedundefinedundefinedundefined
