You can create an array using array syntax:
array = ["first item", {second:'item'}, 3];
array.def = {something:"else"};
alert(array.length);
And here's how you create a multidimensional array using an array of arrays:
array = [
[1,2,3],
[4,5,6],
[7,8,9]
];
alert(array[0][2]); // alerts "3"