Javascript array non undefined element count

Question

I create an array with let arr = new Array(99999) but I don't fill it up to arr.length which is 99999, how can I know how much actual, non undefined elements do I have in this array?

Is there a better way than to look for the first undefined?

Answer 1

You could use Array#forEach, which skips sparse elements.

let array = new Array(99999),
    count = 0;

array[30] = undefined;

array.forEach(_ => count++);

console.log(count);