Gas: How To Change A Global Variable Value And Preserve Its Changed Value When Using The Variable In A Handler Function?

I have this global variable in my script: var targetDocId = 'No doc ID informed yet'; I'm trying to change the value of this global variable inside my main function: function gene

Solution 1:

No theres no such option. You have to use scriptProperties or scriptDb. A global vsriable goes out of scope once your function finishes. Each outside script call starts from zero.

Solution 2:

Each separate execution of a script is done in a new execution instance. Any variables defined outside of a block of code (aka "global" variables) are therefore unique for that instance. When a trigger function is invoked by an event, it runs in its own instance, and any global values it sets are visible only to that instance; another function that is invoked by a spreadsheet or document UI, for example, would have its very own version of that non-scoped object (global).

Definition and retrieval of targetDocId would be a good application of the Cache Service.

function get_targetDocId () {
  var cache = CacheService.getPublicCache();
  var cached = cache.get("targetDocId");
  if (cached != null) {
    return cached;
  }
  var target = createDuplicateDocument(template, docName);  /// Need to add handling for pre-existing documentvar link = target.getUrl();
  var contents = target.getId();
  cache.put("targetDocId", contents, 1500); // cache for 25 minutesreturn contents;
}

Now instead of trying to use a global variable, just call this function:

...
var targetDoc = DocumentApp.openById(get_targetDocId());
...

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Cache Service is one example of persistent storage available for Google Apps Script. The Properties Service was introduced after this answer was written, and is a much lighter-weight way to persist "global" variables between execution instances.

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Observation: it appears that you're using a global (static) for tempate and docName, since there are no parameters for generatePersonDatasheet(). You could simply generate the targetDocId on the fly.

Bug: As it is written, get_targetDocId() will create a new copy of docName every time it needs to refresh the cache (15 mins). You should add handling for the possibility of a pre-existing file. (This is true of your existing onOpen() as well.)