TypeScript generic async function wrapper function

12 September 2021   0 comments   JavaScript

I find this so fiddly! I love TypeScript and will continue to use it if there's a choice. But I just wanted to write a simple async function wrapper and I had to Google for it and nothing was quite right. Here's my simple solution, as an example:

function wrappedAsyncFunction<T>(
    fn: (...args: any[]) => Promise<T>
  ): (...args: any[]) => Promise<T> {
    return async function(...args: any[]) {
      console.time("Took");
      try {
        return await fn(...args);
      } catch(error) {
        console.warn("FYI, an error happened:", error);
        throw error;
      } finally {
        console.timeEnd("Took");
      }

    };
  }

Here's a Playground demo

What I use it for is to wrap my Firebase Cloud Functions so that if any error happens, I can send that error to Rollbar. In particular, here's an example of it in use:

diff --git a/functions/src/cleanup-thumbnails.ts b/functions/src/cleanup-thumbnails.ts
index 46bdb34..a3e8d54 100644
--- a/functions/src/cleanup-thumbnails.ts
+++ b/functions/src/cleanup-thumbnails.ts
@@ -2,6 +2,8 @@ import * as admin from "firebase-admin";
 import * as functions from "firebase-functions";
 import { logger } from "firebase-functions";

+import { wrappedLogError } from "./rollbar-logger";
+
 const OLD_DAYS = 30 * 6; // 6 months
 // const ADDITIONAL_DAYS_BACK = 5;
 // const ADDITIONAL_DAYS_BACK = 15;
@@ -9,7 +11,7 @@ const PREFIX = "thumbnails";

 export const scheduledCleanupThumbnails = functions.pubsub
   .schedule("every 24 hours")
-  .onRun(async () => {
+  .onRun(wrappedLogError(async () => {
     logger.debug("Running scheduledCleanupThumbnails");

...

And my wrappedLogError looks like this:

export function wrappedLogError<T>(
  fn: (...args: any[]) => Promise<T>
): (...args: any[]) => Promise<T> {
  return async function(...args: any[]) {
    try {
      return await fn(...args);
    } catch (error) {
      logError(error);
      throw error;
    }
  };
}

I'm not sure it's the best or correct way to do it, but it seems to work. Perhaps there's a more correct solution but for now I'll ship this because it seems to work fine.

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