What is the proper way to type annotate a standard function in TypeScript?

Considering the provided type definition

export interface MyFun {
  (arg: unknown): unknown;
}

It is straightforward to annotate an arrow function like this:

const arrowF: MyFun = arg => {
  console.log(arg);
}

However, annotating a regular function with the same type raises a question:

function regularF(arg) {
  console.log(arg);
}

The compiler will throw an error message:

Parameter 'arg' implicitly has an 'any' type.

An attempt to specify the type directly in the function declaration does not yield the expected result:

function<MyFun> regularF(arg) {
  console.log(arg);
}

Unfortunately, this approach does not work as intended. For more information, refer to this related issue.

Answer №1

If you annotate your function in this way, it will mimic the behavior of utilizing the MyFun interface:

function newF(parameter: unknown): any {
  console.log(parameter);
}

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