Asynchronous execution for Google App Scripts (gas)

Async.gs

/*
* Async.gs
*
* Manages asyncronous execution via time-based triggers.
*
* Note that execution normally takes 30-60s due to scheduling of the trigger.
*
* @see https://developers.google.com/apps-script/reference/script/clock-trigger-builder.html
*/

var Async = Async || {};
var GLOBAL = this;

// Triggers asynchronous execution of a function (with arguments as extra parameters)
Async.call = function(handlerName) {
  return Async.apply(handlerName, Array.prototype.slice.call(arguments, 1));
};

// Triggers asynchronous execution of a function (with arguments as an array)
Async.apply = function(handlerName, args) {
  var trigger = ScriptApp
  .newTrigger('Async_handler')
  .timeBased()
  .after(1)
  .create();
  CacheService.getScriptCache().put(String(trigger.getUniqueId()), JSON.stringify({ handlerName: handlerName, args: args }));
  return { 
    triggerUid: trigger.getUniqueId(),
    source: String(trigger.getTriggerSource()), 
    eventType: String(trigger.getEventType()), 
    handlerName: handlerName,
    args: args
  };
};

// GENERIC HANDLING BELOW
// 
function Async_handler(e) {
  var triggerUid = e && e.triggerUid;
  var cache = CacheService.getScriptCache().get(triggerUid);
  if (cache) {
    try {
      var event = JSON.parse(cache);
      var handlerName = event && event.handlerName;
      var args = event && event.args;
      if (handlerName) {
        var context, fn = handlerName.split('.').reduce(function(parent, prop) {
          context = parent;
          return parent && parent[prop];
        }, GLOBAL);
        if (!fn || !fn.apply) throw "Handler `" + handlerName + "` does not exist! Exiting..";
        // Execute with arguments
        fn.apply(context, args || []);
      }
    } catch (e) {
      console.error(e);
    }
  }
  // Delete the trigger, it only needs to be executed once
  ScriptApp.getProjectTriggers().forEach(function(t) {
    if (t.getUniqueId() === triggerUid) {
      ScriptApp.deleteTrigger(t);
    }
  });
};

@ShadrinSpock see comment above

Only primitives will work as callback arguments, however its relatively straightforward to pass the ID and then recreate the Spreadsheet object inside the handler method.

https://gist.github.com/sdesalas/2972f8647897d5481fd8e01f03122805?permalink_comment_id=4428924#gistcomment-4428924

In your case you probably want the ID of the folder. Instead of the folder object.

@sdesalas Thank you so much for writing this! I've only just begun my journey as a developer and learned how to write asynchronous functions in Javascript today, only to find that it doesn't work in Google Apps Script. Your library worked like a charm for my purposes though. I managed to get the expected result on the first try, which is honestly incredibly surprising knowing me.

It seems so weird that you can write async function blah(), or return promises and write .then(), but Apps Script still runs it synchronously. Do you know why that is? What is the point of having the syntax if it doesn't work the way it was intended?

@mojoro https://stackoverflow.com/questions/31241396/is-google-apps-script-synchronous