feat: concat

README.md

@@ -54,6 +54,20 @@ const chunkSize = 3;
 ```
 </details>
 
+<details>
+<summary>concat</summary>
+
+```javascript
+import { concat } from '@ilteoood/re-flusso/concat';
+
+concat(
+    fromIterable([1]),
+    fromIterable([2]),
+    fromIterable([3])
+)
+```
+</details>
+
 <details>
 <summary>filter</summary>
 

src/concat.ts

@@ -0,0 +1,24 @@
+export const concat = (...readableStreams: ReadableStream[]) => {
+	const fallbackedStreams = readableStreams ?? [];
+	const readableStreamsLength = fallbackedStreams.length;
+
+	return new ReadableStream({
+		async start(controller) {
+			for (let i = 0; i < readableStreamsLength; i++) {
+				const reader = fallbackedStreams[i].getReader();
+
+				while (true) {
+					const readResult = await reader.read();
+
+					if (readResult.done) {
+						break;
+					}
+
+					controller.enqueue(readResult.value);
+				}
+			}
+
+			controller.close();
+		},
+	});
+};

test/concat.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, test } from "vitest";
+
+import { concat } from "../src/concat";
+import { fromIterable } from "../src/fromIterable";
+import { pipeline } from "../src/pipeline";
+import { toArray } from "../src/toArray";
+
+describe("concat", () => {
+	test("should concat streams", async () => {
+		const destinationArray = [];
+
+		await pipeline(
+			concat(fromIterable([1]), fromIterable([2]), fromIterable([3])),
+			toArray(destinationArray),
+		);
+
+		expect(destinationArray).toEqual([1, 2, 3]);
+	});
+
+	test("should concat streams even if first stream is empty", async () => {
+		const destinationArray = [];
+
+		await pipeline(
+			concat(fromIterable([]), fromIterable([2]), fromIterable([3])),
+			toArray(destinationArray),
+		);
+
+		expect(destinationArray).toEqual([2, 3]);
+	});
+});