can we predict types by function argument passed to it ?
Let's imagine we have fn that will accept one argument (number) and depends on that number I will return collection or single entity from database. Result will differ in model slightly and I would tell to TypeScript that if such number passed to fn argument exists, return me model A otherwise return me model B.
Fn example:
const fn = (id?: number) => {
// body of fn
}
const myCollectionData = fn(); // interface A
const mySingleRecordData = fn(1); // interface B
Cheers!
Sure, you can declare overloads for that function:
const fn: {
(): interfaceA;
(id: number): interfaceB;
} = (id?: number) => {
// body of fn
};
(see Typescript overload arrow functions for this particular syntax)