In order to transform a tuple into the desired object type, we can introduce a generic type called ToOutputType which utilizes a mapped type.
type ToOutputType<T extends { name: string, value: any }[]> = {
[K in T[number] as K["name"]]: { value: K["value"] }
}
Furthermore, we can enhance the functionality of arrayOfObjectsToObject by making it generic.
type Expand<T> = T extends infer O ? { [K in keyof O]: O[K] } : never;
const arrayOfObjectsToObject =
<
T extends { name: K, value: any }[],
K extends string
>(array: readonly [...T]): Expand<ToOutputType<T>> => {
return array.reduce((acc, { name, value }) => {
acc[name] = { value };
return acc;
}, {} as any) as Expand<ToOutputType<T>>;
}
The function parameter T represents the tuple input, while K is utilized to narrow down strings within the tuple to literal types. The return type is specified as
Expand<ToOutputType<T>>
. The
Expand type is mainly used for aesthetic purposes.
Upon calling the function, you will obtain the following result:
const result = arrayOfObjectsToObject([
{ name: 'test', value: 1 },
{ name: 'test2', value: 2 }
]);
const a = result.test
// ^? { value: number; }
const b = result.test2
// ^? { value: number; }
Note that the type of value is inferred as number in both instances. TypeScript automatically broadens the numbers to number, but this behavior can be prevented by using as const.
const result = arrayOfObjectsToObject([
{ name: 'test', value: 1 },
{ name: 'test2', value: 2 }
] as const);
const a = result.test
// ^? { value: 1; }
const b = result.test2
// ^? { value: 2; }
Playground
If avoiding the use of as const is preferred, an additional special generic type for inference can be employed.
type Narrowable = string | number | boolean | symbol | object | undefined | void | null | {};
const arrayOfObjectsToObject =
<
T extends { name: K, value: N }[],
N extends { [k: string]: N | T | [] } | Narrowable,
K extends string
>(array: readonly [...T]): Expand<ToOutputType<T>> => {
return array.reduce((acc, { name, value }) => {
acc[name] = { value };
return acc;
}, {} as any) as Expand<ToOutputType<T>>;
}