Let’s say I defined 2 arrays in JavaScript:

var a1 = new Array(1,2);
var a2 = new Array(3,4);

and a variable :

var a3 = ‘yes’; 

I want to combine these 2 arrays and the variable into a multidimensional array. If you use a standard notation for JavaScript multi-dimensional arrays, you can only refer to array elements by index:

Build a multidimensional array that includes the previously defined arrays a1, a2  and the variable a3:
var  arr = [a1, a2,  a3];

Get the value of the first element in the a1 array: 

alert (arr[0][0]);

You can’t use arr.a1[0]. It will be undefined.

If you want to refer to array elements by name, you need to have an object literal act as a multidimensional array:

Build an object literal: 

var obj = {
  a : a1,
  b : a2,
  c: a3
}

Now you can refer to individual elements as follows:

obj.a[0]

or 

obj.c