Typescript: use type declaration to force a null-check?

Question

I know that you can declare a type as nullable in typescript

But this doesn't force the user to do a null check, e.g.

function maybeReturnString(): string | null { ... }
function getOnlyString(str: string) { ... }

const maybeString = maybeReturnString();
getOnlyString(maybeString) // OK

What's the proper way to make the build fail in case I don't check for null?

Is there something similar to Option[String] in Scala or String? in Kotlin?

emeraldsanto · Accepted Answer · 2020-09-06 14:21:35Z

1

I'm not sure which version of TypeScript you're running but that should definitely throw a compile time error, as demonstrated in this playground (using your own code).

To answer your other question, you can also use the string? syntax which is equivalent to string | undefined.

answered Sep 6, 2020 at 14:21

emeraldsanto

4,7611 gold badge17 silver badges28 bronze badges

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

1 Comment

Dotan Over a year ago

Weird, checking

Dotan · Accepted Answer · 2020-09-06 15:23:50Z

0

My issue was that I didn't set the config strictNullChecks=true

answered Sep 6, 2020 at 15:23

Dotan

7,77214 gold badges39 silver badges53 bronze badges

Collectives™ on Stack Overflow

Typescript: use type declaration to force a null-check?

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related