juliendargelos · July 9, 2025 10:28 · Jul 9, 2025 · Jul 9, 2025
diff --git a/concurrent.ts b/concurrent.ts
@@ -3,10 +3,10 @@
  * concurrency limit. A concurrency limit equal to Infinity makes this function
  * behave like `Promise.all`.
  *
- * @params items - List of items to process.
- * @params run - Function to run for each item, which returns a Promise.
- * @params concurrency - Maximum number of concurrent executions.
- * @return A Promise that resolves to an array of results.
+ * @params items - List of items to process
+ * @params run - Asynchronous function to run for each item
+ * @params concurrency - Maximum number of concurrent executions
+ * @return A Promise that resolves to an array of results
  */
 async function concurrent<Item = any, Result = any>(
   items: Iterable<Item>,

diff --git a/concurrent.ts b/concurrent.ts
@@ -0,0 +1,28 @@
+/**
+ * Concurrently run an asynchronous function on a list of items given a
+ * concurrency limit. A concurrency limit equal to Infinity makes this function
+ * behave like `Promise.all`.
+ *
+ * @params items - List of items to process.
+ * @params run - Function to run for each item, which returns a Promise.
+ * @params concurrency - Maximum number of concurrent executions.
+ * @return A Promise that resolves to an array of results.
+ */
+async function concurrent<Item = any, Result = any>(
+  items: Iterable<Item>,
+  run: (item: Item, index: number) => Promise<Result>,
+  concurrency: number = Infinity
+): Promise<Result[]> {
+  const pool: (() => void)[] = []
+  concurrency = Math.max(1, Math.floor(concurrency || 0))
+
+  return Promise.all([...items].map((item, index) => (
+    new Promise<Result>((resolve, reject) => {
+      const start = () => run(item, index)
+        .then((result) => { pool.pop()?.(), resolve(result) })
+        .catch((error) => { pool.splice(0), reject(error) })
+
+      index < concurrency ? start() : pool.unshift(start)
+    })
+  )))
+}
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