How to check an element in an array for 'undefined'?

Question

Node.js

I understand the question is funny, but when I check an element in an array for "undefined": I get an error something like "Cannot read property '-1' of undefined" when j = i = -1. That's how I can check the existence of an index in an array. if (typeof array[j][i] == 'undefined')

Answer 1

if (j in array && i in array[j])