API · Consume

single()

Resolve with zero or one value, and reject when the stream produces more.

Example

const user = await exstream(users)
  .find((user) => user.id === id)
  .single()

Cardinality

An empty stream resolves with undefined; one value resolves with that value. A second value aborts the consumer branch and rejects with error code EXSTREAM_MORE_THAN_ONE_VALUE.

single() always returns a promise and consumes through normal end to prove that no second value exists. Use head().single() when you want the first value without enforcing cardinality on the original output.

Unhandled record errors, fatal failures, and aborts reject the promise.

Signature

single(): Promise<T | undefined>

Related

head(), last(), toArray()