svelte/documentation/tutorial/08-stores/05-custom-stores/text.md

title
Custom stores

As long as an object correctly implements the subscribe method, it's a store. Beyond that, anything goes. It's very easy, therefore, to create custom stores with domain-specific logic.

For example, the count store from our earlier example could include increment, decrement and reset methods and avoid exposing set and update:

function createCount() {
	const { subscribe, set, update } = writable(0);

	return {
		subscribe,
		increment: () => update((n) => n + 1),
		decrement: () => update((n) => n - 1),
		reset: () => set(0)
	};
}