Typescript type of intersection of all objects in array of unknown length

Question

I have a type of an array of object in Typescript. Let's say:

type Arr = [{ toto: string}, {titi: number}];

I don't know the length in advance. I would like to have the type of the merge of all objects in the array, ie the intersection

{
  toto: string,
  titi: number
}

Thanks!

I've tried Arr[number] but this gave us the union {toto: string}|{toto:number} — Guillaume Wuip
– Guillaume Wuip, Commented Oct 9, 2019 at 18:56

Titian Cernicova-Dragomir · Accepted Answer · 2019-10-09 19:07:05Z

3

As you discovered, you can use Arr[number] to get a union of all types in the array. You can then use UnionToIntersection described here to convert it to a intersection :

type Arr = [{ toto: string}, {titi: number}];
type UnionToIntersection<U> = 
  (U extends any ? (k: U)=>void : never) extends ((k: infer I)=>void) ? I : never

type All = UnionToIntersection<Arr[number]>

answered Oct 9, 2019 at 19:07

Titian Cernicova-Dragomir

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1 Comment

Guillaume Wuip Over a year ago

Very nice :) I was trying to write something recursive. Thanks a lot !

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