Typescript: How can I check multiple variables are nullish?

Question

Context

I made isNullish function to check a specific variable is null or undefined. This function is implemented like below.

type Nullish = null | undefined;
const isNullish = (target: unknown): target is Nullish => target == null;

Problem

I use this utility in many places, but it is annoying when to check many variables.

if (isNullish(v1) || isNullish(v2) || isNullish(v3)......) {}

In this situation, how can I achieve better solution for this? I'm not good at typescript, so it maybe easy question. Sorry for this and thanks for your reading.

Use an array instead of so many standalone variables, usually — CertainPerformance
– CertainPerformance, Commented Jun 18, 2021 at 4:31
@CertainPerformance When I made array util, type is not inferred by VSCode — undefined
– undefined, Commented Jun 18, 2021 at 4:41
@undefined Inside the if block, either v1, v2 or v3 is/are Nullish, so TypeScript cannot narrow the type of any variable to Nullish type and thus all the variables will still be infered as unknown. — Alvin Leung
– Alvin Leung, Commented Jun 18, 2021 at 4:52

blaumeise20 · Accepted Answer · 2021-06-18 05:10:13Z

1

Something like this:

if ([v1, v2, v3].some(isNullish)) {}

or for better readability:

if ([v1, v2, v3].some((v) => isNullish(v)) {}

edited Jun 18, 2021 at 5:10

blaumeise20

2,23011 silver badges26 bronze badges

answered Jun 18, 2021 at 4:47

Mr_Green

42k48 gold badges171 silver badges277 bronze badges

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

2 Comments

undefined Over a year ago

I already used this solution, but type is not inferred by VSCode.

Mr_Green Over a year ago

Maybe v1, v2, v3 doesn't have type unknown.

Collectives™ on Stack Overflow

Typescript: How can I check multiple variables are nullish?

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related