mceachen · July 11, 2020 21:14 · Jul 11, 2020
diff --git a/thenCollect.ts b/thenCollect.ts
@@ -0,0 +1,23 @@
+export type SyncOrAsync<T> = T | Promise<T>
+export type Maybe<T> = T | undefined
+export type MaybeSyncOrAsync<T> = Maybe<SyncOrAsync<Maybe<T>>>
+
+/**
+ * Serialized promise gathering and compaction
+ */
+export async function thenCollect<T1, T2>(
+  arr: MaybeSyncOrAsync<MaybeSyncOrAsync<T1>[]>,
+  f: (t: T1) => MaybeSyncOrAsync<T2>
+): Promise<T2[]> {
+  const result: T2[] = []
+  for (const eaP of toA(await arr)) {
+    if (eaP != null) {
+      const ea = await eaP
+      if (ea != null) {
+        const r = await f(ea)
+        if (r != null) result.push(r)
+      }
+    }
+  }
+  return result
+}