在 typescript 中重用 function 重载

Question

How to reuse function overloading in typescript?

For example, I have some function that is overloaded

function apply(value: number): number;
function apply(value: string): string;

function apply(value: any): any {
    return value;
}

And some other function that uses the apply function

function apply2(value: number | string) {
    return apply(value); // getting 'No overloads matching this call' here
}

const result = apply2(1);

Do I need to overload apply2, too?

• type of result must be number
• generics are not the option (an example is simplified)

Answer 1

The reason is that type number | string number | string is neither assignable to type number , nor to string . This way the compiler does not know which overload you're using in apply2 , and thus it cannot tell you what the return type of apply2 will be.

So, yes, the only way to solve this is by overloading the apply2 function