array.splice vs setting a value to null

Question

You should use array.splice(i, 1); instead of array[i] = null This will preserve the keys in the array

Source : Should I bother cleaning array in node.js?

I don't really understand this sentence. Why array[i] = null will change the keys of the array ? Why array.splice(i, 1); is better ?

See also [JavaScript Array Delete Elements](https://stackoverflow.com/questions/500606/javascript-array-delete-elements) — Bergi, Oct 28 '15 at 11:02
It is not better at all. All depends what is the goal you want to achieve. — webduvet, Oct 28 '15 at 11:09
If you want to squeeze out performance then setting it to null is the better option (V8 optimizes arrays, and fiddling with the indices prevents it from optimizing it properly). If you need to remove an item from an array then using `splice` is the way to go. Depends on what you want to do. — Sverri M. Olsen, Oct 28 '15 at 11:11

Tushar · Accepted Answer · 2015-10-28T11:05:17.563

array.splice(i, 1); will remove the element from array, so changing the length of array.

Whereas array[i] = null will just set the value at the index i to null and will not alter the array length. This is same as delete array[i] except the delete operator will set the value at the index to undefined.

Regarding

Why array[i] = null will change the keys of the array?

I think there is missing a word not in between the will and change.

So, according to me, it should be

Why array[i] = null will not change the keys(or rather length) of the array?

Second question:

Why array.splice(i, 1); is better?

It alters the length of the array by removing the element from it. So, when iterating over array you don't have to check if(value == null).

Which one to use totally depends on the use-case.

So i believe `splice` is not really better. Just a different usage. Thanks. — Magus, Oct 28 '15 at 10:59
@Magus: In fact, `splice` is magnitudes slower, because it has to adjust all the indices. — Bergi, Oct 28 '15 at 11:03

score 0 · Answer 2 · answered Oct 28 '15 at 11:05

It's fairly easy to see the differences in behaviour with a simple test case. This is what Chrome outputs from the console:

var test = ['a','b','c']
test[1] = null
["a", null, "c"]

var test = ['a','b','c']
test.splice(1, 1)
["a", "c"]

var test = ['a','b','c']
delete test[1]
["a", undefined × 1, "c"]

As you can see, splice is the only one to change the index of c from 2 to 1.

Which one you want to use depends on your use case. There may be a case where you have a fixed-length array, and you want to remove an item without affecting the index of items after it, in which case splicing would be inappropriate.

array.splice vs setting a value to null

2 Answers2

Linked