post: addendum

src/posts/apps-script-async-await.md

@@ -135,6 +135,46 @@ This output works as expected:
 
 So, it is clear that the WebAssembly API is running asynchronously and not blocking the task queue.
 
+## Addendum: `setTimeout` and `Utilities.sleep`
+
+The functions `setTimeout` and `setInterval` are typically used to create asynchronous behavior in JavaScript. However, in Apps Script, these functions are not defined and will result in `ReferenceError: setTimeout is not defined`.
+
+It may be tempting to use `Utilities.sleep()` to create asynchronous behavior to recreate `setTimeout`, but this function is synchronous and will block the task queue. 
+
+```javascript
+new Promise((resolve, reject) => {
+    console.log("start");
+    Utilities.sleep(2000);
+    console.log("end");
+    resolve();
+  }).then(() => console.log("done"));
+console.log("next");
+```
+
+This will output the following:
+
+```sh
+3:20:21 PM	Notice	Execution started
+3:20:22 PM	Info	start
+3:20:24 PM	Info	end
+3:20:24 PM	Info	next < this is printed after the sleep!!!
+3:20:24 PM	Info	done
+3:20:24 PM	Notice	Execution completed
+```
+
+If this was asynchronous, the `next` would be printed before the `end`. 
+
+Interestingly, if you use `async`/`await`, the output changes to:
+
+```sh
+3:22:37 PM	Notice	Execution started
+3:22:38 PM	Info	start
+3:22:40 PM	Info	end
+3:22:40 PM	Info	done
+3:22:40 PM	Info	next < this is printed after the sleep!!!
+3:22:40 PM	Notice	Execution completed
+```
+
 ## Conclusion
 
 The topic here is a bit esoteric, but as you attempt to push the limits of what is possible in Apps Script, it is good to know that you can use Promises, async and await in your code. I hope to share much more in the future on WebAssembly and other advanced topics in Apps Script!