Move collection to store module

packages/store/src/getter.ts

@@ -0,0 +1,20 @@
+import {Readable, Writable} from "svelte/store"
+
+export const getter = <T>(store: Readable<T>) => {
+  let value: T
+
+  store.subscribe((newValue: T) => {
+    value = newValue
+  })
+
+  return () => value
+}
+
+export type WritableWithGetter<T> = Writable<T> & {get: () => T}
+export type ReadableWithGetter<T> = Readable<T> & {get: () => T}
+
+export function withGetter<T>(store: Writable<T>): WritableWithGetter<T>
+export function withGetter<T>(store: Readable<T>): ReadableWithGetter<T>
+export function withGetter<T>(store: Readable<T> | Writable<T>) {
+  return {...store, get: getter<T>(store)}
+}