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June 16, 2019 06:16
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Typescript making undefined properties optional
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| /** | |
| * Get the keys of the properties to which U can be assigned. | |
| */ | |
| type AssignableKeys<T, U> = { | |
| [K in keyof T]: U extends T[K] ? K : never | |
| }[keyof T]; | |
| /** | |
| * Get the interface containing only properties to which undefined can be assigned. | |
| */ | |
| type UndefinableProperties<T> = { | |
| [K in AssignableKeys<T, undefined>]: T[K] | |
| } | |
| /** | |
| * Get all of the keys except those to which U can be assigned. | |
| */ | |
| type IncompatibleKeys<T, U> = { | |
| [K in keyof T]: U extends T[K] ? never : K | |
| }[keyof T]; | |
| /** | |
| * Get the interface containing no properties to which undefined can be assigned. | |
| */ | |
| type OmitUndefinableProperties<T> = { | |
| [K in IncompatibleKeys<T, undefined>]: T[K] | |
| } | |
| /** | |
| * Get the interface where all properties are optional. | |
| */ | |
| type Optional<T> = {[K in keyof T]?: T[K]}; | |
| /** | |
| * Get the interface where properties that can be assigned undefined are | |
| * also optional. | |
| */ | |
| type UndefinedOptional<T> = OmitUndefinableProperties<T> & Optional<UndefinableProperties<T>>; |
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