TS2394
This overload signature is not compatible with its implementation signature.
Broken Code ❌
The implementation does not match all signatures:
function sum(a: number, b: number): number;
function sum(a: string, b: string): string;
function sum(a: number | string, b: number | string) {
return `${parseInt(a + '', 10) + parseInt(b + '', 10)}`;
}Fixed Code ✔️
To match the first function overload, we have to add code to our function body which can also return a number:
function sum(a: number, b: number): number;
function sum(a: string, b: string): string;
function sum(a: number | string, b: number | string) {
if (typeof a === 'number' && typeof b === 'number') {
return a + b;
}
return `${parseInt(a + '', 10) + parseInt(b + '', 10)}`;
}