Count of “Defined” Array Elements

Question

Given following array:

var arr = [undefined, undefined, 2, 5, undefined, undefined];

I\'d like to get the count of elements which are

Answer 1

An array length is not the number of elements in a array, it is the highest index + 1. length property will report correct element count only if there are valid elements in consecutive indices.

var a = [];
a[23] = 'foo';
a.length;  // 24

Saying that, there is no way to exclude undefined elements from count without using any form of a loop.