Function scan

scan<T, R>(
scanner: (accumulator: R, chunk: T) => SyncOrAsync<R>,
initialValue: R,
): TransformStream<T, R>
Create a TransformStream that produces a stream of accumulated values
Type Parameters
- T
- R
Parameters
- scanner: (accumulator: R, chunk: T) => SyncOrAsync<R>
  The scanner function to apply to each chunk
- initialValue: R
  The initial value for the scan
Returns TransformStream<T, R>
A TransformStream that emits each intermediate accumulated value
Example
```
// Calculate running sum
const stream = readable.pipeThrough(scan((acc, x) => acc + x, 0));
// If readable emits [1, 2, 3], the result will be [1, 3, 6]
```
- Defined in index.ts:395