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vjau/isExactOptional.ts

Created September 16, 2023 13:01
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Utility Typescript Type to know when exactOptionalPropertyTypes is set
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isExactOptional.ts
type _Intersect = {a?:number} & {a:number|undefined};
//state of exactOptionalPropertyTypes
type IsExactOptional = _Intersect["a"] extends Exclude<_Intersect["a"], undefined> ? true : false;
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vjau commented Mar 16, 2025

Doesnt work past Typescript 4.6, but is easily replaced by

type IsExactOptional = {foo: undefined} extends {foo?:number} : false : true;

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