A simple function that marks a callback as busy to avoid calling it multiple times before it has finished its task.

busy.ts

const busyCallbacks = new Set()

export async function busy(callback : () => any) : Promise<any> {
  if (busyCallbacks.has(callback)) {
    return
  }
  busyCallbacks.add(callback)
  const value = await callback()
  busyCallbacks.delete(callback)
  return value
}