CODEWITHSUNDEEP
typescript
Antoine
Antoine

Reputation: 58

Typescript partial interface overloading is choosing wrong overload

When I am trying to define an overload my function with a Partial interface overloading, typescript is picking the wrong overload

interface Args {
  _id: string;
  name: string;
}
interface Result {
  _id: string;
  name: string;
}

function myFunction(arg: Args): Result;
function myFunction(arg: Partial<Args>): Partial<Result> {
  return arg;
}

// Argument of type '{ _id: string; }' is not assignable to parameter of type 'Args'.
// Property 'name' is missing in type '{ _id: string; }' but required in type 'Args'
myFunction({ _id: 'aa' });

Trying to use myFunction({ _id: 'aa' } as Partial<Args>); doesn't help

How could I make this work ?

Upvotes: 2

Views: 156

Answers (1)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249606

The last signature is the implementation signature and is not part of the publicly accessible signatures. So your function really on has one accessible signature function myFunction(arg: Args): Result; hence the error.

function myFunction(arg: Args): Result;
function myFunction(arg: Partial<Args>): Partial<Result>
function myFunction(arg: Partial<Args>): Partial<Result> {
  return arg;
}

myFunction({ _id: 'aa' });// ok now

Playground Link

Upvotes: 2

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