Question

I was reading a book about Javascript and saw this line;

JavaScript does not support true multidimensional arrays, but you can
approximate them with arrays of arrays.

What’s the difference?

Answer 1

A true multi-dimensional array must be indexed with multiple indices. An array of arrays can be indexed with a single index, which will return another array. A true multi-dimensional array stores all its data contiguously. An array of arrays stores all its constituent arrays arbitrarily scattered around. This can improve iteration performance because of cache effects for true arrays.