add: concurrency batches samples

data_structures/js_questions/concurrency/batch_fetch.ts

@@ -0,0 +1,24 @@
+async function fetchUsersBatch(batch: number[]): Promise<string[]> {
+  return new Promise<string[]>((resolve) => {
+    setTimeout(() => {
+      resolve(batch.map((id) => `User ${id}`));
+    }, 2000);
+  });
+}
+
+async function batchFetchUsers(totalUsers: number, batchSize: number) {
+  const message = 'Batch Fetching Time';
+  console.time(message);
+
+  const userIds = Array.from({ length: totalUsers }, (_, i) => i + 1);
+  const batches: number[][] = [];
+
+  for (let i = 0; i < userIds.length; i++) {
+    batches.push(userIds.slice(i, i + batchSize));
+  }
+
+  const allResults = await Promise.all(batches.map((batch) => fetchUsersBatch(batch)));
+  console.log(allResults.flat());
+  console.timeEnd(message);
+}
+batchFetchUsers(10, 2);

data_structures/js_questions/concurrency/why_use_promise_all.ts

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+async function fetchUsers() {
+  return new Promise<string>((resolve) => setTimeout(() => resolve('User Data'), 2000));
+}
+
+async function fetchPosts() {
+  return new Promise<string>((resolve) => setTimeout(() => resolve('Product Data'), 3000));
+}
+
+/**
+ * Sequential Time: 5005.678ms
+ * Total Time: 5 seconds (because each await waits for the previous one to finish).
+ */
+async function fetchDataSequentital() {
+  const message = 'Sequential time';
+  console.time(message);
+
+  const users = await fetchUsers();
+  const posts = await fetchPosts();
+
+  console.log({ users, posts });
+  console.timeEnd(message);
+}
+
+/**
+ * Parallel Time: 3002.456ms
+ * - Total Time: 3 seconds (instead of 5s)!
+ * - ✅ Use Promise.all() whenever tasks are independent and can run in parallel.
+ * - ✅ It makes execution faster than multiple sequential await calls! 🚀
+ */
+async function fetchDataParallel() {
+  const message = 'Parallel Time';
+  console.time(message);
+
+  const [user, posts] = await Promise.all([fetchUsers(), fetchPosts()]);
+
+  console.log({ user, posts });
+  console.timeEnd(message);
+}
+fetchDataParallel();