3.6.1 Creating Arrays
If you pass only a single number to the Array( ) constructor, it specifies the length of the array. Thus:
var a = new Array(10);
creates a new array with 10 undefined elements.
3.6.2 Array Literals
var matrix = [[1,2,3], [4,5,6], [7,8,9]];
var base = 1024; var table = [base, base+1, base+2, base+3];
var sparseArray = [1,,,,5];