Function: first()

first<T>(predicate?): Operator<T, T>

Creates a stream operator that emits only the first element from the source stream that matches an optional predicate.

This operator is designed to find a specific value and then immediately terminate.

If a predicate function is provided, the operator will emit the first value for which the predicate returns a truthy value.
If no predicate is provided, it will simply emit the very first value from the source.

After emitting a single value, the operator completes. If the source stream completes before a matching value is found, an error is thrown.

Type Parameters

T = any

The type of the values in the source stream.

(value) => MaybePromise<boolean>

An optional function to test each value. It receives the value and should return true to indicate a match.

An Operator instance that can be used in a stream's pipe method.

Throws an error with the message "No elements in sequence" if no matching value is found before the source stream completes.