Typescript Object type to Array type

user_2265812 0
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What is the correct way to transform an object type to an array of objects, each one containing one key of the object ?

For instance I want to transform 

type MyObjectType = {
    foo: number,
    bar: string
}

into

type MyObjectArrayType = { key: 'foo', value: number} | { key: 'bar', value: string}

so that I can do 

const objects: MyObjectArrayType[] = [{key: 'foo', value: 2}, {key: 'bar', value: 'baz'}]

I was thinking about something like 

type MyObjectArrayType<K extends keyof MyObjectType> = { value: MyObjectType[K], key: K }

but can't get it to work like I want.

typescript-typings typescript
1 Answers

You can use a mapped type to generate each member of the union (for each property) and the use an index type to get all the value types in the mapped type.

type MyObjectType = {
    foo: number,
    bar: string
}

type PropUnion<T> = {
  [K in keyof T]: { value: T[K], key: K }
}[keyof T]

type MyObjectArrayType = PropUnion<MyObjectType>;
const objects: MyObjectArrayType[] = [{key: 'foo', value: 2}, {key: 'bar', value: 'baz'}]

Playground Link

user_1257340
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