How to destructure an array with elements of different types in typescript

Question

The following code example works fine in javascript:

 const f = ()=> { return[true,"text",11]; }
 const [active,status,numberEleven] = f();
 const twelve = numberEleven + 1;

However, const twelve = numberEleven + 1; throws an error in typescript because numberEleven could be either a string, a boolean or a number:
I've tried to change the function return types:

const f = ()=> {
  const res: [boolean, string, number] = [true, warning, score];
  return res;
}

But it didn't work. I then tried to change the type of the deconstructed array like so:

 const [active,status,numberEleven]: [boolean, string, number] = f();

But this approach resulted in the following error:

Type '(string | number | boolean)[]' is not assignable to type '[boolean, string, number]'.
  Target requires 3 element(s) but source may have fewer.

So, what's the best way to destructure an array with elements of different types in typescript?
Thanks!

Your second option works (typescriptlang.org/play?#code/…) The other version would be a as const: typescriptlang.org/play?#code/… — Titian Cernicova-Dragomir
– Titian Cernicova-Dragomir, Commented Nov 24, 2021 at 19:02
Please consider reviewing the guidelines for How to Ask and what constitutes a minimal reproducible example. When you show code and something is not working about it, it doesn't help to just say "but it didn't work". It is expected that you describe exactly what is not working... is there an error message? If so, what is it and where does it happen? Is there some unexpected output? What and where? Since the version you say "didn't work" actually does work in the TS Playground, right now the problem isn't reproducible and thus the question might be closed unless you rectify it. Good luck! — jcalz
– jcalz, Commented Nov 24, 2021 at 20:04

emeraldsanto · Accepted Answer · 2021-11-26 15:02:28Z

1

This can be achieved using as const.

const f = () => {
  return [true, "text", 11] as const;
}

const [active,status,numberEleven] = f();
const twelve = numberEleven + 1;

answered Nov 26, 2021 at 15:02

emeraldsanto

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Comments

chipimix · Accepted Answer · 2021-11-26 13:39:19Z

0

Indeed, the second option works. The error I shared was being caused by another block of code. thanks Dragomir! <3

answered Nov 26, 2021 at 13:39

chipimix

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