Function singletonPromiseFn

Create singleton promise function, it can be called only once.

And later you can reset it to make it can be called again.

Example

it('should singletonPromiseFn works', async() => {
   let dummy = 0

   const fn = vi.fn(async() => {
     await sleep(10)
     dummy += 1
     return dummy
   })

   const promise = singletonPromiseFn(fn)
   expect(dummy).toBe(0)
   expect(fn).toBeCalledTimes(0)

   const res = await promise()
   expect(res).toBe(1)
   expect(fn).toBeCalledTimes(1)
   expect(dummy).toBe(1)

   // call wrapper again, but not call fn again, because it's staled
   const res1 = await promise()
   expect(res1).toBe(1)
   expect(fn).toBeCalledTimes(1)
   expect(await promise()).toBe(1)
   expect(fn).toBeCalledTimes(1)
   expect(dummy).toBe(1)

   // reset staled promise, make it can be called again
   await promise.reset()
   // call wrapper again, and call fn again
   const res2 = await promise()
   expect(res2).toBe(2)
   expect(fn).toBeCalledTimes(2)
   expect(dummy).toBe(2)
 })