How to debug Google Apps Script (aka where does Logger.log log to?)

Question

In Google Sheets, you can add some scripting functionality. I\'m adding something for the onEdit event, but I can\'t tell if it\'s working. As far as I can tell

Answer 1

If you have the script editor open you will see the logs under View->Logs. If your script has an onedit trigger, make a change to the spreadsheet which should trigger the function with the script editor opened in a second tab. Then go to the script editor tab and open the log. You will see whatever your function passes to the logger.

Basically as long as the script editor is open, the event will write to the log and show it for you. It will not show if someone else is in the file elsewhere.

Answer 2

2017 Update: Stackdriver Logging is now available for Google Apps Script. From the menu bar in the script editor, goto: View > Stackdriver Logging to view or stream the logs.

console.log() will write DEBUG level messages

Example onEdit() logging:

function onEdit (e) {
  var debug_e = {
    authMode:  e.authMode,  
    range:  e.range.getA1Notation(),    
    source:  e.source.getId(),
    user:  e.user,   
    value:  e.value,
    oldValue: e. oldValue
  }

  console.log({message: 'onEdit() Event Object', eventObject: debug_e});
}

Then check the logs in the Stackdriver UI labeled onEdit() Event Object to see the output

Answer 3

As far as I can tell, you can't debug a live event from google docs, so you have to do it from the debugger, which is pointless since the event argument passed to my onEdit() function will always be undefined if I run it from the Script Editor.

True - so define the event argument yourself for debugging. See How can I test a trigger function in GAS?

I was trying to use the Logger.log method to log some data whenever the onEdit function gets called, but this too seems like it only works when run from the Script Editor. When I run it from the Script Editor, I can view the logs by going to View->Logs...

True again, but there is help. Peter Hermann's BetterLog library will redirect all logs to a spreadsheet, enabling logging even from code that is not attached to an instance of the editor / debugger.

If you're coding in a spreadsheet-contained script, for example, you can add just this one line to the top of your script file, and all logs will go to a "Logs" sheet in the spreadsheet. No other code necessary, just use Logger.log() as you usually would:

Logger = BetterLog.useSpreadsheet();

Answer 4

It's far from elegant, but while debugging, I often log to the Logger, and then use getLog() to fetch its contents. Then, I either:

• save the results to a variable (which can be inspected in the Google Scripts debugger—this works around cases where I can't set a breakpoint in some code, but I can set one in code that gets executed later)
• write it to some temporary DOM element
• display it in an alert

Essentially, it just becomes a JavaScript output issue.

It grossly lacks the functionality of modern console.log() implementations, but the Logger does still help debug Google Scripts.

Answer 5

I am having the same problem, I found the below on the web somewhere....

Event handlers in Docs are a little tricky though. Because docs can handle multiple simultaneous edits by multiple users, the event handlers are handled server-side. The major issue with this structure is that when an event trigger script fails, it fails on the server. If you want to see the debug info you'll need to setup an explicit trigger under the triggers menu that emails you the debug info when the event fails or else it will fail silently.

Answer 6

I've gone through these posts and somehow ended up finding a simple answer, which I'm posting here for those how want short and sweet solutions:

1. Use console.log("Hello World") in your script.
2. Go to https://script.google.com/home/my and select your add-on.
3. Click on the ellipsis menu on Project Details, select Executions.

4. Click on the header of the latest execution and read the log.