writable 
Auto unsubscribe on destory for writable.
Usage 
<script>
  import { writable } from '@svelte-use/core'
  const count = writable(0)
</script>
Type Declarations 
export declare function writable<T>(
  value?: T,
  start?: StartStopNotifier<T>
): Writable<T>
Source 
Source • Docs