How to handle JS destructing assignment with one of the array element is null?

Question

I am trying to use the array destructing assignment to get the results from Promise.all(). Here is my code:

const[_, resFunc2] = await Promise.all([
      func1(),
      func2(),
    ]);

func1 doesn't return any value, and func2 returns a value which will be assigned to resFunc2. I want to ask what's the best practice for handling the result of func1 since func1 doesn't return any value? Thanks a lot~

Do you mean that func1 returns a promise that resolve in null? — Federkun
– Federkun, Commented May 16, 2019 at 21:06
Have you tried using Array#filter to remove undefined values? .filter(x => x !== undefined) — nick zoum
– nick zoum, Commented May 16, 2019 at 21:08
Reverse the order of the promises and then deconstruct to just one array value. Ignoring the second value as it will be discarded. — Reactgular
– Reactgular, Commented May 16, 2019 at 21:11

Michael Lorton · Accepted Answer · 2019-05-16 23:10:44Z

2

Have you considered the simplest possibility?

const resFunc2 = (await Promise.all([
      func1(),
      func2(),
    ]))[1];

If you are insistent on destructuring (I have to admit, it's super-cool), you could do this.

const [resFunc2] = await Promise.all([
      func2(),
      func1(),
]);

edited May 16, 2019 at 23:10

answered May 16, 2019 at 23:00

Michael Lorton

44.7k26 gold badges111 silver badges159 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Moritz Roessler · Accepted Answer · 2019-05-16 23:09:36Z

2

There are a variety of possibilities, depending on what you need to do with the result.

You can use default values if you need a specific value.

const [_ = 0, resFunc2] = await Promise.all([
      func1(),
      func2(),
]);

You can omit it if you don't need it at all

const [, resFunc2] = await Promise.all([
      func1(),
      func2(),
]);

_{Disclaimer: I didn't test any of these}

edited May 16, 2019 at 23:09

answered May 16, 2019 at 22:55

Moritz Roessler

8,67329 silver badges57 bronze badges

3 Comments

Michael Lorton Over a year ago

I really like your second solution. I didn't know that was even allowed. Almost as good as mine :-). I didn't know about the first possibility either, but I don't think it fits the need. The third one can go wrong too many ways.

Moritz Roessler Over a year ago

Thank you :) - I agree with you on all points! - I like the second one because it expresses its intent quite readable. - number three doesn't make much sense, i'll better remove it, thanks for the feedback.

Michael Lorton Over a year ago

I came up with a (fourth? fifth?) solution! Still enamored of the empty-comma syntax though.

Collectives™ on Stack Overflow

How to handle JS destructing assignment with one of the array element is null?

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related