Creates an iterator whose values are the result of applying the callback to the values from this iterator and then flattening the resulting iterators or iterables.
method
url.URLSearchParamsIterator.flatMap
callback: (value: T, index: number) => Iterator<U, unknown, undefined> | Iterable<U, unknown, undefined>
): IteratorObject<U, undefined, unknown>;
@param callback
A function that accepts up to two arguments to be used to transform values from the underlying iterator into new iterators or iterables to be flattened into the result.