Can Svelte export all store's Typescript definitions?

[sangxxh]

Is your feature request related to a problem? Please describe.

Take this simple store as an example:

import { readable, Readable } from 'svelte/store';

const store: Readable<string> = readable('', (set) => {
    helper(set);
})

function helper(set) {
    set('test');
}

The problem is that I can't type helper's argument and return types because there are some internal Svelte types that are not exported:

/** Callback to inform of a value updates. */
type Subscriber<T> = (value: T) => void;

/** Unsubscribes from value updates. */
type Unsubscriber = () => void;

This applies to many other internal types in svelte/store, too, ie. The below is not exported:

/** Start and stop notification callbacks. */
type StartStopNotifier<T> = (set: Subscriber<T>) => Unsubscriber | void;

Describe the solution you'd like

I would like to be able to write:

function helper(set: Subscriber<string>): Unsubscriber | void {
    set('test');
}

The same would apply to other features of Svelte, too.
This means Svelte would have to export (almost) all of its Typescript definitions in svelte/store

Describe alternatives you've considered

I've looked at Type Inference but that's fairly inconvenient for dev. I'd prefer to directly use Svelte's internal type definitions.

How important is this feature to you?

I'm looking for a way to use Typescript with Svelte efficiently. This would help a lot with using Typescript in Svelte.

Additional context
Note that I haven't used Svelte a lot. There are maybe better Typescript practices for this Svelte use case that someone can advise?

[dreitzner]

Type definitions should be available here, but I am afraid not for the store:
https://github.com/pyoner/svelte-typescript/tree/master/packages/types

Why would you use a helper function outside of the subscriber function?
Inside the scope the type would persist and make your live easier....

[sangxxh]

Type definitions should be available here, but I am afraid not for the store:
https://github.com/pyoner/svelte-typescript/tree/master/packages/types

Why would you use a helper function outside of the subscriber function?
Inside the scope the type would persist and make your live easier...

Sometimes we need that for code organization.
There's a REPL from Svelte that does the same:

• https://svelte.dev/repl/dcc69ccad6c341e8b75ee38c3eac1524?version=3.20.1

Using Typescript Declaration Merging to manually export those store types is the best work around at the moment.
Not sure how the Svelte team would approach to provide better Typescript DX?

I also feel like we need a Svelte Typescript Cheatsheet (like the React Typescript one)

[cereschen]

I have the same need.
There are many types that are not exported, which makes working with TypeScript difficult.

[dreitzner]

Some further info:

• store types are located at node_modules\svelte\types\runtime\store\index.d.ts
• the export for some of the types is not set

I can think of 2 things that could be done:

1. Create a github action to automatically port the types to https://github.com/pyoner/svelte-typescript/tree/master/packages/types (or create a svelte/types repo)
2. export them by default (for this it might be a good idea to create a namespace for svelte to not clash with other types from external libaries that might be imported)

[sangxxh]

Some further info:

• store types are located at node_modules\svelte\types\runtime\store\index.d.ts
• the export for some of the types is not set

I can think of 2 things that could be done:

1. Create a github action to automatically port the types to https://github.com/pyoner/svelte-typescript/tree/master/packages/types (or create a svelte/types repo)
2. export them by default (for this it might be a good idea to create a namespace for svelte to not clash with other types from external libaries that might be imported)

Option 2 is ideal.
Option 1 is a workaround and it also introduces another package into one's project, I want to avoid that.

[sangxxh]

Inspected further and there are some store types that are only internally useful and don't need to be exported. Check out the PR link above