feat(flushPromises): add flushPromises function

Author: lambdalisue

deno.jsonc

@@ -6,6 +6,7 @@
     "./async-value": "./async_value.ts",
     "./barrier": "./barrier.ts",
     "./ensure-promise": "./ensure_promise.ts",
+    "./flush-promises": "./flush_promises.ts",
     "./lock": "./lock.ts",
     "./mutex": "./mutex.ts",
     "./notify": "./notify.ts",
@@ -36,6 +37,7 @@
     "@core/asyncutil/async-value": "./async_value.ts",
     "@core/asyncutil/barrier": "./barrier.ts",
     "@core/asyncutil/ensure-promise": "./ensure_promise.ts",
+    "@core/asyncutil/flush-promises": "./flush_promises.ts",
     "@core/asyncutil/lock": "./lock.ts",
     "@core/asyncutil/mutex": "./mutex.ts",
     "@core/asyncutil/notify": "./notify.ts",

flush_promises.ts

@@ -0,0 +1,25 @@
+/**
+ * Flush all pending promises in the microtask queue.
+ *
+ * ```ts
+ * import { flushPromises } from "@core/asyncutil/flush-promises";
+ *
+ * let count = 0;
+ * Array.from({ length: 5 }).forEach(() => {
+ *   Promise.resolve()
+ *     .then(() => count++)
+ *     .then(() => count++);
+ * });
+ *
+ * console.log(count); // 0
+ * await flushPromises();
+ * console.log(count); // 10
+ * ```
+ *
+ * The original idea comes from [flush-promises] package in npm.
+ *
+ * [flush-promises]: https://www.npmjs.com/package/flush-promises
+ */
+export function flushPromises(): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve));
+}

flush_promises_test.ts

@@ -0,0 +1,18 @@
+import { test } from "@cross/test";
+import { assertEquals } from "@std/assert";
+import { flushPromises } from "./flush_promises.ts";
+
+test(
+  "flushPromises() flushes all pending promises in the microtask queue",
+  async () => {
+    let count = 0;
+    Array.from({ length: 5 }).forEach(() => {
+      Promise.resolve()
+        .then(() => count++)
+        .then(() => count++);
+    });
+    assertEquals(count, 0);
+    await flushPromises();
+    assertEquals(count, 10);
+  },
+);