Leverage the power of function overloading in TypeScript for efficient code

How can function overloading be reused effectively in TypeScript?

Consider a scenario where a function is overloaded:

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

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

Now, let's say there is another function that uses the apply function:

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

const result = apply2(1);

Is it necessary to overload apply2 as well?

  • The type of result should be number
  • Using generics is not an option in this case (the example provided is simplified)

Answer №1

The issue here lies in the fact that the type number | string is not compatible with either type number or string. As a result, the compiler cannot determine which overload of apply2 you are utilizing, leading to ambiguity regarding the return type of apply2.

Therefore, the only resolution to this problem is to create overloads for the apply2 function.

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