What is the Process for Integrating TypeScript into a Hook Function in SvelteKit?

Question

What is the Process for Integrating TypeScript into a Hook Function in SvelteKit?

In my SvelteKit application's hooks.ts file, I currently have the following code:

export async function handle({ event, resolve }) {
  console.log(event.locals) //<-- Works fine
}

I am now exploring how to implement types for the event and resolve parameters. Based on my understanding, the event parameter can be typed as follows:

import type { RequestEvent } from '@sveltejs/kit'

export async function handle(event: RequestEvent, resolve: ???){
  ...
}

However, I am struggling to determine how to type the resolve parameter. The documentation provides this example:

interface Handle {
  (input: {
    event: RequestEvent;
    resolve(
      event: RequestEvent,
      opts?: ResolveOptions
    ): MaybePromise<Response>;
  }): MaybePromise<Response>;
}

Based on my knowledge of TypeScript, it seems like resolve is a function with two parameters that returns a promise. How should I incorporate this into the declaration of the handle function?

typescript svelte sveltekit

Answer 1

Answer №1

It seems like the question you're asking (or should be asking 😁) is: "How can I inform TypeScript that my function should be classified as type Handle?".

A straightforward solution would involve assigning the function to a variable, allowing for easier typing.

export const handle: Handle = async function ({ event, resolve }) {
  console.log(event.locals);
}

One thing to note is that there's no need to individually type event or resolve, as TypeScript already recognizes the argument and return types of your function. If your current implementation doesn't return a MaybePromise<Response>, TypeScript will highlight this discrepancy.

Answer 2

It seems like the question you're asking (or should be asking 😁) is: "How can I inform TypeScript that my function should be classified as type Handle?".

A straightforward solution would involve assigning the function to a variable, allowing for easier typing.

export const handle: Handle = async function ({ event, resolve }) {
  console.log(event.locals);
}

One thing to note is that there's no need to individually type event or resolve, as TypeScript already recognizes the argument and return types of your function. If your current implementation doesn't return a MaybePromise<Response>, TypeScript will highlight this discrepancy.

Answer 3

Answer №2

If you prefer not to type the function in its entirety, you have the option to separately define the arguments and return type while still using the export async function syntax.

Keep in mind that the argument type doesn't come with a name, so you'll need to manually extract it from Handle. Despite appearances, there's actually only one argument being destructured. For example:

// Consider exporting this from another location to avoid duplication
type HandleParams = Parameters<Handle>[0];

export async function handle({ event, resolve }: HandleParams) : Promise<Response> {
    // ...
}

The original return type makes use of MaybePromise<T> to accommodate both synchronous and asynchronous returns. You should stick to using just Promise if the function is truly async.

There's also a handy helper type like Parameters that lets you genericallly extract the return type from Handle:

type HandleResult = ReturnType<Handle>;

Answer 4

If you prefer not to type the function in its entirety, you have the option to separately define the arguments and return type while still using the export async function syntax.

Keep in mind that the argument type doesn't come with a name, so you'll need to manually extract it from Handle. Despite appearances, there's actually only one argument being destructured. For example:

// Consider exporting this from another location to avoid duplication
type HandleParams = Parameters<Handle>[0];

export async function handle({ event, resolve }: HandleParams) : Promise<Response> {
    // ...
}

The original return type makes use of MaybePromise<T> to accommodate both synchronous and asynchronous returns. You should stick to using just Promise if the function is truly async.

There's also a handy helper type like Parameters that lets you genericallly extract the return type from Handle:

type HandleResult = ReturnType<Handle>;

Answer 5

Answer №3

Eliminate the 'any' warnings by incorporating 'satisfies Handle' into your function.

import type { Handle } from '@sveltejs/kit';

export const handle = (async ({ event, resolve }) => {
  if (event.url.pathname.startsWith('/custom')) {
    return new Response('custom response');
  }

  const response = await resolve(event);
  return response;
}) satisfies Handle;

Find more information here:

To view accurate examples, ensure TypeScript is enabled by clicking on this link:

https://i.sstatic.net/YaAtR.png

Answer 6

Eliminate the 'any' warnings by incorporating 'satisfies Handle' into your function.

import type { Handle } from '@sveltejs/kit';

export const handle = (async ({ event, resolve }) => {
  if (event.url.pathname.startsWith('/custom')) {
    return new Response('custom response');
  }

  const response = await resolve(event);
  return response;
}) satisfies Handle;

Find more information here:

To view accurate examples, ensure TypeScript is enabled by clicking on this link:

https://i.sstatic.net/YaAtR.png

What is the Process for Integrating TypeScript into a Hook Function in SvelteKit?

Answer №1

Answer №2

Answer №3

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