How dynamic array access work?

In C if i declare int x[4]

Which tells me its an integer array with each array element size fixed of size 4.

So after initialization when I access x[3] : address of array +element size which is 2 * index => (x[3]=2000+2*3) Assuming 2000 is the array address

In Javascript

We have

var a=[3,"rohan",6] //Dynamically typed

Here array elements are not equally sized for eg.a[2] is a string whose element size is different than a[0] which is an integer

So how does the array access work?