配列リテラルで空の配列を作り、後から要素を追加

var 変数名 = [];

変数名[0] = 値;

<script type="text/javascript">
var $arrayNum = [];
$arrayNum[0] = 2;
$arrayNum[1] = 5;
$arrayNum[2] = 10;
document.write( $arrayNum[0] + '<br />' );
document.write( $arrayNum[1] + '<br />' );
document.write( $arrayNum[2] + '<br />' );
</script>

<script type="text/javascript">
var $arrayStr = [];
$arrayStr[0] = 'a';
$arrayStr[1] = 'b';
$arrayStr[2] = 'c';
document.write( $arrayStr[0] + '<br />' );
document.write( $arrayStr[1] + '<br />' );
document.write( $arrayStr[2] + '<br />' );
var $arrayStr = [];
$arrayStr[0] = '文字列Ａ';
$arrayStr[1] = '文字列Ｂ';
$arrayStr[2] = '文字列Ｃ';
document.write( $arrayStr[0] + '<br />' );
document.write( $arrayStr[1] + '<br />' );
document.write( $arrayStr[2] + '<br />' );
</script>