To declare an empty two-dimensional array in JavaScript, we use the map method.
For instance, we write
const arr = [...Array(3)].map(() => Array(5));
to create an array with 3 empty slots with Array(3).
And then we spread them to a new array.
Then we call map with a callback that returns an array with 5 empty slots created with Array(5).
We now have a 3×5 empty 2d array.
