Automatic type inference in function parameters in Typescript

When attempting to infer the type of Data based on input parameters, it correctly infers when the data is an object type; however, it defaults to 'unknown' when the data is a function type. https://i.sstatic.net/wkuQa.png

declare function getTypeOf<Data>(options: { data: Data }): any;

getTypeOf({
  data() {
    return {
      name: "123",
      age: 1,
    };
  },
  getData() {
    return {
      name: 123,
    };
  },
});

It seems that changing the data to an object or including getData in the type parameters resolves this issue. Still, I'm looking for documentation explaining why this behavior occurs. https://i.sstatic.net/6H39d.png

Any insights or documentation references would be greatly appreciated.

Answer №1

If you want to determine the type of argument required

function findArgumentType<T>(t: T): T { return t; }

In this scenario, you specifically need the data property

function fetchArgumentData<T extends {data: unknown}>(t: T): T['data'] { return t.data; }

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