在打字稿界面中使用泛型并分配给箭头功能

Question

[Edited] I have a quick question on typescript generics, what I am trying to achieve is writing a generic function to insert an array of items of some kind into a firebase database. I don't know in advance the array I will receive, so I wrote this function and it works: if I define an arrow function using the generic type I have no errors:

export const seedInitialDatas = async <T>(
  userUid: string,
  collectionName: string,
  itemsToSeed: T[]
): Promise<void> => {
  itemsToSeed.forEach(async (itemToSeed) => {
    await firestore
      .collection("users")
      .doc(userUid)
      .collection(collectionName)
      .add(itemToSeed);
  });
};

now, instead of having the types defined directly in the function I would like to have a type of an interface to define it:

type SeedInitialData<T> = (userUid: string, collectionName: string, itemsToSeed: T[]) =>Promise<void>;

export const seedInitialDatas: SeedInitialData = async (
  userUid,
  collectionName,
  itemsToSeed
) => {
  itemsToSeed.forEach(async (itemToSeed) => {
    await firestore
      .collection("users")
      .doc(userUid)
      .collection(collectionName)
      .add(itemToSeed);
  });
};

if I do this I receive an error: Generic type 'SeedInitialData' require 1 argument of type

Answer 1

I'm not 100% sure what you're trying to do but making your function into a type or interface is pretty easy:

type s<Items> = (userUid: string, collectionName: string, itemsToSeed: Items[]) => void;

export const seedInitialDatas: s<string> = async (
    userUid,
    collectionName,
    itemsToSeed
): Promise<void> => { };

or as interface:

interface s<Items> { 
    (userUid: string, collectionName: string, itemsToSeed: Items[]): void
};

export const seedInitialDatas: s<string> = async (
    userUid,
    collectionName,
    itemsToSeed
): Promise<void> => { };

Although I'd suggest you using the type as normally interfaces are used for objects

Answer 2

I just resolved, I was assinging type T to the type definition instead of the function:

type SeedInitialData = <T>(
  userUid: string,
  collectionName: string,
  itemsToSeed: T[]
) => Promise<void>;

export const seedInitialDatas: SeedInitialData = async (
  userUid,
  collectionName,
  itemsToSeed
) => {
  itemsToSeed.forEach(async (itemToSeed) => {
    await firestore
      .collection("users")
      .doc(userUid)
      .collection(collectionName)
      .add(itemToSeed);
  });
};