Why am I getting an error with this multidimensional array?

Question

I'm still new to Javascript and trying to understand multi-dimensional arrays. Why does the following code work?

var occupied = [[],[]];
occupied[1][0] = 0;
console.log(occupied[1][0]);

Answer 1

That's because you have defined only two items in your array (index 0 and index 1). So there is no index 2.

Answer 2

Size of your occupied array is 2 . So the maximum index you can access is 1. If you try to access any index above 1 it means that you are accessing undefined.

here occupied[2][0] is undefined and you cannot store anything inside undefined , which is causing you an error :)

Answer 3

occupied[1][0] = 0;<\/code> works because the length of occupied<\/code> is 2. occupied[1]<\/code> will access the second node, which is an empty array occupied[1][0] = 0;<\/code> this will assign 0 to the first element of the second node of occupied<\/code> array.

works because the length of occupied<\/code> is 2. occupied[2]<\/code> will try to access the third node occupied<\/code> array, which donot exist. In this case occupied[2]<\/code> is undefined. occupied[2][0] = 0;<\/code> will try to set 0 to zeroth index of an undefined variable, this will throw a refrence errror like