Optional object property that must be a spesific type and can't be undefined

[babakfp]

🔎 Search Terms

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🕗 Version & Regression Information

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⏯ Playground Link

https://www.typescriptlang.org/play?#code/C4TwDgpgBAsiAq5oF4BQUNQD5QN5QDsBDAWwgC4oBnYAJwEsCBzKAX3Ux32LMpoeYBuKAHswweiOIAbSnQCu0dqgDGUmlBIgAakWmKoyPBww8KUAEQWANCdHjJMyvIIATCADNGEV9agB6fygAdQB5ACUAaQBlPwAhAFV4KABJKABRAA0ABXSAYWSU5PhQjPDwiNR2IA

💻 Code

type MyType =
    | { name: string }
    | { name: string; optional: true }

🙁 Actual behavior

const myValue = {
    name: "",
    optional: undefined, // WORKS
}

🙂 Expected behavior

const myValue = {
    name: "",
    optional: undefined, // ERROR: Type 'undefined' is not assignable to type 'true'.
}

Additional information about the issue

I don't know if this should be a bug report or a feature request.

[fatcerberus]

Not a bug. { name: "", optional: undefined } is assignable to { name: string } due to structural subtyping. You're looking for #12936.

[fatcerberus]

Optional object property that must be a [specific] type and can't be undefined

The above having been said: if this is your only use case for the requested behavior, then you can get that simply by enabling exactOptionalPropertyTypes.
https://www.typescriptlang.org/tsconfig#exactOptionalPropertyTypes

[typescript-bot]

This issue has been marked as "Question" and has seen no recent activity. It has been automatically closed for house-keeping purposes.