Is there a way to unwrap from optional variable?

Question

Is there a way to "unwrap" variables returned by reload method?

let reloadProps: ReloadProps | undefined;

if (useClientSide() === true) {
    reloadProps = reload(props.eventId);
}

const {
    isTiketAdmin,
    jwt,
    userFbId,
    organizationId,
    organization,
    event,
    enableSaleSwitch,
    enableSaleSwitchOnWordpress,
    permission,
} = reloadProps;

Now I got this error:

./pages/[lang]/event/[...eventId].tsx:72:5
Type error: Property 'isTiketAdmin' does not exist on type 'ReloadProps | undefined'.

  70 |   }
  71 |   const {
> 72 |     isTiketAdmin,
     |     ^
  73 |     jwt,
  74 |     userFbId,
  75 |     organizationId,
error Command failed with exit code 1.

`if (reloadProps) { ... }`? Right now that will clearly fail if `useClientSide` returns false, for example. If reload always returns an object in the client-side case, why use reloadProps at all, for that matter; just do `if (useClientSide()) { const { isTiketAdmin, ... } = reload(props.eventId); ... }`. — jonrsharpe, Aug 08 '21 at 07:21

score 0 · Accepted Answer · answered Aug 08 '21 at 07:23

0

The main problem is, that the values you want to get out of reloadProps are not available if is undefined. You have to check that the value is not undefined beforehand:

if (reloadProps !== undefined) {
  const {
    isTiketAdmin,
    jwt,
    userFbId,
    organizationId,
    organization,
    event,
    enableSaleSwitch,
    enableSaleSwitchOnWordpress,
    permission,
  } = reloadProps;
}

This way the compiler can infer, that the type is not ReloadProps | undefined anymore but ReloadProps only and then you can access the values.

answered Aug 08 '21 at 07:23

Peter Lehnhardt

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Will values available out of if statement? – János Aug 08 '21 at 07:25
No. Out of the if statement `reloadProps` is `undefined`. Therefore no values. – Peter Lehnhardt Aug 08 '21 at 07:26
1

@János const (like let) is _block_ scoped, so no. I'd strongly recommend getting familiar with basic JavaScript before trying to add the complexity of TypeScript and a framework like Next.js on top. – jonrsharpe Aug 08 '21 at 07:26
wouldn't it be better to check `reloadProps != null` so that null and undefined are checked? Or better yet just `if (reloadProps)` – theZ3r0CooL Sep 09 '22 at 22:26
@TheN3wbie Yes, definitely. Good catch! – Peter Lehnhardt Sep 12 '22 at 12:07

Is there a way to unwrap from optional variable?

1 Answers1