Asynchronous execution of a function App Script

There is another way to accomplish this.

You can use time-based one-off triggers to run functions asynchronously, they take a bit of time to queue up (30-60 seconds) but it is ideal for slow-running tasks that you want to remove from the main execution of your script.

// Creates a trigger that will run a second later
ScriptApp.newTrigger("myFunction")
  .timeBased()
  .after(1)
  .create();

There is handy script that I put together called Async.gs that will help remove the boilerplate out of this technique. You can even use it to pass arguments via the CacheService.

Here is the link:

https://gist.github.com/sdesalas/2972f8647897d5481fd8e01f03122805

// Define async function
function runSlowTask(user_id, is_active) {
  console.log('runSlowTask()', { user_id: user_id, is_active: is_active });
  Utilities.sleep(5000);
  console.log('runSlowTask() - FINISHED!')
}

// Run function asynchronously
Async.call('runSlowTask');

// Run function asynchronously with one argument
Async.call('runSlowTask', 51291);

// Run function asynchronously with multiple argument
Async.call('runSlowTask', 51291, true);

// Run function asynchronously with an array of arguments
Async.apply('runSlowTask', [51291, true]);

// Run function in library asynchronously with one argument
Async.call('MyLibrary.runSlowTask', 51291);

// Run function in library asynchronously with an array of arguments
Async.apply('MyLibrary.runSlowTask', [51291, true]);

• You want to execute functions by the asynchronous processing using Google Apps Script.
• You want to run the functions with the asynchronous processing using time trigger.

If my understanding is correct, unfortunately, there are no methods and the official document for directly achieving it. But as a workaround, that can be achieved by using both Google Apps Script API and the fetchAll method which can work by asynchronous processing.

The flow of this workaround is as follows.

1. Deploy API executable, enable Google Apps Script API.
2. Using fetchAll, request the endpoint of Google Apps Script API for running function.
   • When several functions are requested once, those work with the asynchronous processing by fetchAll.

Note:

• I think that Web Apps can be also used instead of Google Apps Script API.
• In order to simply use this workaround, I have created a GAS library. I think that you can also use it.
• In this workaround, you can also run the functions with the asynchronous processing using time trigger.

References:

• fetchAll
• Deploy the script as an API executable
• scripts.run of Google Apps Script API
• Benchmark: fetchAll method in UrlFetch service for Google Apps Script
• GAS library for running the asynchronous processing

If I misunderstand your question, I'm sorry.

With the new V8 runtime, it is now possible to write async functions and use promises in your app script.

Even triggers can be declared async! For example (typescript):

async function onOpen(e: GoogleAppsScript.Events.SheetsOnOpen) {
    console.log("I am inside a promise");
    // do your await stuff here or make more async calls
}

To start using the new runtime, just follow this guide. In short, it all boils down to adding the following line to your appsscript.json file:

{
  ...
  "runtimeVersion": "V8"
}