Using optional chaining with array.entries

Question

Just trying to understand optional chaining and unsure if it can be used in the following situation with .entries, that is:

for (const [index, val] of Array.from(myArray)?.entries()) {
  if (val.status === 1) {
      . . . 
       . . . 
  }
}

I basically don't want to proceed if myArray is empty.

It doesn’t do anything in that situation. Array.from never returns null or undefined. But if an array is empty, iterating over it doesn’t do anything anyway. — Ry-
– Ry- ♦, Commented Mar 16, 2022 at 3:32
@Ry- Appreciate the explanation. So if myArray is empty to begin with, then this part of the code will not crash out - correct? — ArthurJ
– ArthurJ, Commented Mar 16, 2022 at 3:39
Right. And if it’s already an array, there’s no need to use Array.from either. — Ry-
– Ry- ♦, Commented Mar 16, 2022 at 4:43

Nick Vu · Accepted Answer · 2022-03-16 04:57:11Z

1

If you look for a short null check, I think your problem is not from Array.from but it's from myArray variable. If myArray is undefined, Array.from(myArray)?.entries() will throw an error

const myArray = undefined
const entries = Array.from(myArray)?.entries() //throw an error

If you want to overcome this, you need to use short circuit evaluation to assign the default value [] whenever myArray is undefined or null

const myArray = undefined
const entries = Array.from(myArray || []).entries() //working!

If myArray is already an array (or possibly an undefined value), you can get rid of Array.from too

const myArray = undefined
const entries = myArray?.entries() || [] //assign a default value for your loop

edited Mar 16, 2022 at 4:57

answered Mar 16, 2022 at 4:10

Nick Vu

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