How to handle objects that can be null in Typescript?

Question

I want a function to return either an object or null.

Here is how I handle it today:

export interface MyObject {
    id: string
}

function test(id) : MyObject | null {
    if (!id) {
        return null;
    }

    return {
        id: id
    }
}

Is this best practice?

I would prefer to make the interface nullable rather than returning MyObject | null.

But I don't know if that is possible.

Seems like it not possible and you did the best option : github.com/Microsoft/TypeScript/issues/23477 — BenoitVasseur
– BenoitVasseur, Commented Jan 31, 2019 at 14:16

Paleo · Accepted Answer · 2019-01-31 15:05:06Z

2

Is this best practice?

It's just fine. Everybody does that (or with undefined).

I would prefer to make the interface nullable rather than returning MyObject | null.

You can do:

export type NullableObject = null | {
  id: string
}

It is uncommon but fine too.

edited Jan 31, 2019 at 15:05

answered Jan 31, 2019 at 14:04

Paleo

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Comments

Jonas Høgh · Accepted Answer · 2019-01-31 13:40:31Z

1

In Typescript, null and undefined are part of the domains of all types, unless strict null checks are enabled. In my opinion, explicitly declaring nulls is a much better practice than having them everywhere implicitly, but in the real world it is often not realistic to enable strict mode when interoperating with library code that isn't designed for it.

answered Jan 31, 2019 at 13:40

Jonas Høgh

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1 Comment

user1283776 Over a year ago

Do you think I am already following best practice or is there a better way to explicitly declare nulls?

Kamil Kiełczewski · Accepted Answer · 2019-01-31 13:38:42Z

0

This should handle null case too (if --strictFunctionTypes compiler option is off)

function test(id) : MyObject {
    if (!id) {
        return null;
    }

    return {
        id: id
    }
}

edited Jan 31, 2019 at 13:38

answered Jan 31, 2019 at 13:33

Kamil Kiełczewski

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2 Comments

user1283776 Over a year ago

Thanks! However, I don't think I want to turn that off yet. I don't know TypeScript well enough to start turning things off.

Kamil Kiełczewski Over a year ago

@user1283776 more info about your question is here

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