看php, 太随意了：
<?php
$a = array();
$a[0] = 1;
$a[1] = 2;
print_r($a);
?>
<?php
$a[0] = 1;
$a[1] = 2;
print_r($a);
?>
再看js:
<html>
<body>
<script>
var myArray = new Array();
myArray[0]="1";
myArray[1]="2";
myArray[2]="3";
alert(myArray[0]);
</script>
</body>
</html>
<html>
<body>
<script>
myArray[0]="1";
myArray[1]="2";
myArray[2]="3";
alert(myArray[0]);
</script>
</body>
</html>