I'm currently writing a function that takes two arguments. The first being the key of an enum, and the second depends on the first argument.
Some of the keys don't require a second argument, so when I assign undefined in the payload map, the function explicity requires to pass in undefined.
Is there a way I can pass in the first key, and not pass in a second argument, while fulfilling the type requirements?
Code:
export enum MyKey {
BleepBloop = 'BleepBloop',
BeepBoop = 'BeepBoop',
BingBong = 'BingBong',
}
export type SubstitutionsMap = {
[MyKey.BleepBloop]: [string, string];
[MyKey.BeepBoop]: [string, string];
[MyKey.BingBong]: undefined;
};
export const getFoo = <K extends MyKey>(key: K, substitutions: SubstitutionsMap[K]): string => {
// Handle private logic
return ''
};
getFoo(MyKey.BingBong) // <--- Error is here
Error:
(enum member) MyKey.BingBong = "BingBong"
Expected 2 arguments, but got 1.ts(2554)
index.ts(13, 49): An argument for 'substitutions' was not provided.
This error is gone when I explicitly pass in undefined, but I would like to not have to pass in a second argument if it's just undefined.
This fixes my error:
getFoo(MyKey.BingBong, undefined)
You could create function overloads for getFoo that matches your required types.
Something like below:
function getFoo(key: MyKey.BingBong): string;
function getFoo<K extends MyKey.BeepBoop | MyKey.BleepBloop>(
key: K,
substitutions: SubstitutionsMap[K]
): string;
function getFoo(key: MyKey, substitutions?: SubstitutionsMap): string {
if (key === MyKey.BingBong) {
// code in which I don't need substitutions
}
if (substitutions) {
// code in which I do need to access substitutions
}
return '';
}
getFoo(MyKey.BleepBloop); //error!
getFoo(MyKey.BleepBloop, ['asd', 'qwe']); //fine
getFoo(MyKey.BeepBoop); //error!
getFoo(MyKey.BeepBoop, ['asd', 'qwe']); //fine
getFoo(MyKey.BingBong); //fine
getFoo(MyKey.BingBong, ['asd', 'qwe']); //error!
This will make it so that when the first argument is MyKey.BingBong, it will not let you pass a second argument, but if it is another member of MyKey, it will require you to pass a second argument.