Append data to an array otherwise create one in ES6

Question

I have this code:

  if (typeof my.nested.dataset !== "undefined") {
    my.nested.dataset.push(data);
  } else {
    my.nested.dataset = [data];
  }

I need to push data to an array but only if the array exists otherwise I need to create one.

I'm repeating my.nested.dataset three times. What alternatives do I have to append/assign at once.

Possible duplicate of [javascript: check if array exist, if not create it](https://stackoverflow.com/questions/1961528/javascript-check-if-array-exist-if-not-create-it) — Rajesh, Feb 21 '18 at 06:00
The answer below is more concise although the more important question is do you call that code in more than one place. If so, you should really put the code into a function say function addToNestedDataset(data). Then it doesn't really matter that your code is a bit more verbose as it is easier for the next perhaps less experience developer to read and understand. — Andrew, Feb 21 '18 at 06:00

Suren Srapyan · Accepted Answer · 2018-02-21T06:05:31.080

3

You can initialize your dataset via my.nested.dataset = my.nested.dataset || [].

And then in the code you don't need to check with if. Just call push on it

 my.nested.dataset.push(data);

In one line

(my.nested.dataset = my.nested.dataset || []).push(data)

edited Feb 21 '18 at 06:05

answered Feb 21 '18 at 05:56

Suren Srapyan

Can I do it in one line like you did before the edit (`(my.nested.dataset || []).push(data)`)? – isar Feb 21 '18 at 06:03
In that case you need to put appropriate `()`. I have edited – Suren Srapyan Feb 21 '18 at 06:05
Should we not close as dupe? – Rajesh Feb 21 '18 at 06:23

score 1 · Answer 2 · answered Feb 21 '18 at 06:04

1

If you want to use a one-liner, it's

(my.nested.dataset = my.nested.dataset || []).push(data);

but that still repeats my.nested. If it's a really long name, make a helper variable for it. You cannot avoid repeating .data.

answered Feb 21 '18 at 06:04

Bergi

Should we not close as dupe? – Rajesh Feb 21 '18 at 06:23
I have already marked it as dupe. Hope it justifies the question's scope – Rajesh Feb 21 '18 at 08:37

2 Answers2