I add a element to the array in a higher position than its length
I wonder if is there a way to access or delete this empty elements, I think it can waste memory
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No, it's not wasting memory. Only the elements that are assigned use memory, see the linked question. – Barmar Oct 23 '18 at 20:44
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You could just not write to a position larger than the length of the array.. that is why `push` exists. – Gabriele Petrioli Oct 23 '18 at 20:45
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When doing this, you create a "sparse array". The items in between the non-null entries contain undefined. As such, the memory footprint is negligible. You cannot delete them. If you don't like this behavior, just don't create sparse arrays.
Scott Marcus
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For filtering non sparse/dense elements, you could use a callback which returns for every element true.
Maybe this link helps a bit to understand the mechanic of a sparse array: JavaScript: sparse arrays vs. dense arrays.
let array = new Array(99999),
nonsparse;
array[30] = undefined;
nonsparse = array.filter(_ => true);
console.log(nonsparse);
console.log(nonsparse.length);
Nina Scholz
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But this really doesn't address the question. *I wonder if is there a way to access or delete this empty elements, I think it can waste memory* – Scott Marcus Oct 23 '18 at 20:47
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do you mention the memory part? if yes, the yes ... i like tautologies, but *"I wonder if is there a way to ... delete this empty elements"* – Nina Scholz Oct 23 '18 at 20:48
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I mentioned both parts. Your answer just shows how to create a second array with the non-undefined data from the first. It doesn't address either points. – Scott Marcus Oct 23 '18 at 20:50