fix state

src/internal/StreamStageBuilder.ts

@@ -39,9 +39,9 @@ export function MappedAsyncStreamBuilder<T, U>(
   maxConcurrency: number,
   mapFn: (t: T) => Promise<U>,
 ) {
-  let concurrency = 0
   return {
     build() {
+      let concurrency = 0
       return [
         ...prev.build(),
         new stream.Transform({
@@ -81,9 +81,9 @@ export function MappedAsyncUnorderedStreamBuilder<T, U>(
   maxConcurrency: number,
   mapFn: (t: T) => Promise<U>,
 ) {
-  let concurrency = 0
   return {
     build() {
+      let concurrency = 0
       const promises: Set<Promise<unknown>> = new Set()
       return [
         ...prev.build(),
@@ -120,9 +120,9 @@ export function MappedAsyncUnorderedStreamBuilder<T, U>(
 }
 
 export function BatchedStreamBuilder<T>(prev: StreamStageBuilder<T>, batchSize: number) {
-  let currentBatch: T[] = []
   return {
     build() {
+      let currentBatch: T[] = []
       return [
         ...prev.build(),
         new stream.Transform({
@@ -173,9 +173,10 @@ export function FilteredStreamBuilder<T>(prev: StreamStageBuilder<T>, predicate:
 }
 
 export function ThrottledStreamBuilder<T>(prev: StreamStageBuilder<T>, elements: number, perDurationMs: number) {
-  let timestamps: number[] = []
   return {
     build() {
+      let timestamps: number[] = []
+
       return [
         ...prev.build(),
         new stream.Transform({