How to Create Dynamic Multidimensional Array?

I need to create a 3D array that can be resized per-dimension. My first thought was to create a 1D array and “simulate” the 3D array (like thing[(height*y)+x] or whatever it is) but I don’t believe that would allow for resizing. I googled it but all I could find was how to make static multidimensional arrays.

How would I achieve this in JavaScript/UnityScript?

I know with c# you can create Lists that allow for resizing.