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Removing 'optional' attributes from a type's properties disallow adding undefined as it's type

See original GitHub issue

Bug Report

🔎 Search Terms

type generic remove optional attribute

🕗 Version & Regression Information

I did test this on 4.4.4 and 4.5.0-beta using playground

⏯ Playground Link

Playground link with relevant code

💻 Code

type NullableType<T> = {
    [K in keyof T]-?: undefined extends T[K]
    ? T[K] | null | undefined
    : T[K]
}

🙁 Actual behavior

Removing optional attribute from type also remove undefined from final type (when not removing optional attribute, final type is x?: typeof x | null | undefined)

🙂 Expected behavior

Removing optional attribute just removes the optional attribute and doesn’t modify final type

Issue Analytics

State:
Created 2 years ago
Comments:6 (3 by maintainers)

Top GitHub Comments

1reaction

MartinJohnscommented, Nov 18, 2021

Sounds like a duplicate of #31025.

0reactions

KuShcommented, Nov 22, 2021

@KuSh does the relatively new compiler option exactOptionalPropertyTypes make it behave the way you are expecting?

It seems so. But is effectively too recent for my current project (which use TS 4.3) and also has other consequencies as we’re used to set optional props as undefined (outside of NullableTypes). Thanks for tip I’ll keep that in mind 👍