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typescriptfunctionconstantstypescript-genericssignature
Ole
Ole

Reputation: 519

How to write an async function with a generic type without using const

Is it possible to write this code without using export const, but rather export async function?

This is a sample of the code, heavily simplified:

interface Product {
  id: string;
  name: string;
}

type Listener<Subject, Payload extends object> = (event: {
  subject: Subject;
  payload?: Partial<Payload>;
}) => Promise<void>;

export const onEvent: Listener<Product, never> = async (event) => {
  await new Promise(function (resolve) {
    
    // a simplified example of using the parameters
    console.log(event.subject.id, event.subject.name);

    setTimeout(resolve, 1000);
  });
};

I'm wondering if it's possible to write this in the form of

export async function onEvent ... {

Without breaking it down into, for example

export async function onEvent(event: { subject: Product; payload?: never }): Promise<void> {


It doesn't seem like it after reading the current Typescript docs.

Upvotes: 0

Views: 504

Answers (1)

matt helliwell
matt helliwell

Reputation: 2678

Basically, no there isn't. With the 'function' keyword, the type is derived from the arguments and return type, you can't separately specify the type. You could do

export const onEvent: Listener<Product, never> = async function (event) {...}

but that's about it.

Upvotes: 1

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