46 lines
1.7 KiB
TypeScript
46 lines
1.7 KiB
TypeScript
/**
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* Utility type to force use of all properties of T.
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*
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* Similar to Required<T> build-in type, but allows `undefined` values.
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*/
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type AllProps<T> = T & {
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[P in keyof T]-?: unknown;
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};
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/**
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* Helper function to check listed properties according to given type. Check if all properties has been used when object is initialised.
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*
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* Example use:
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*
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* ```ts
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* type SomeType = { propA: string; propB?: number; }
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*
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* // propB has to be mentioned even it is optional. It still should be initialized with undefined.
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* const a: SomeType = requireAllProps<SomeType>({ propA: "value A", propB: undefined });
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*
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* // checked type is implicit for variable.
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* const b = requireAllProps<SomeType>({ propA: "value A", propB: undefined });
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* ```
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*
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* Wrong use of this helper:
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*
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* 1. Omit checked type - all checked properties will be expect as of type never
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*
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* ```ts
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* type SomeType = { propA: string; propB?: number; }
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* // const z: SomeType = requireAllProps({ propC: "no type will work" }); // Property 'propA' is missing in type '{ propC: string; }' but required in type 'SomeType'.
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* ```
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*
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* 2. Apply to spreaded object - there is no way how to check in compile time if spreaded object contains all properties
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*
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* ```ts
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* type SomeType = { propA: string; propB?: number; }
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* const y: SomeType = { propA: "" }; // valid object according to SomeType declaration
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* // const x = requireAllProps<SomeType>({ ...y }); // Argument of type '{ propA: string; propB?: number; }' is not assignable to parameter of type 'AllProps<SomeType>'.
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* ```
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*
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* @param obj object to check if all properties has been used
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* @returns untouched obj parameter is returned
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*/
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export declare function requireAllProps<T>(obj: AllProps<T>): T;
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export {};
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