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  you can t debug a live event from Google Sheets  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   So  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- gt Logs     I was hoping I d be able to see the logs from when the event actually gets executed  but I can t figure it out   How do I debug this stuff

User · Answer

Currently you are confined to the container bound nature of using scripts within docs. If you create a new script inside outside of docs then you will be able to export information to a google spreadsheet and use it like a logging tool.

For example in your first code block

function setCheckboxes() {

    // Add your spreadsheet data
    var errorSheet = SpreadsheetApp.openById('EnterSpreadSheetIDHere').getSheetByName('EnterSheetNameHere');
    var cell = errorSheet.getRange('A1').offset(errorSheet.getLastRow(),0);

    // existing code
    var checklist = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("checklist");
    var checklist_data_range = checklist.getDataRange();
    var checklist_num_rows = checklist_data_range.getNumRows();

    // existing logger
    Logger.log("checklist num rows: " + checklist_num_rows);

   //We can pass the information to the sheet using cell.setValue()
    cell.setValue(new Date() + "Checklist num rows: " + checklist_num_rows);

When I'm working with GAS I have two monitors ( you can use two windows ) set up with one containing the GAS environment and the other containing the SS so I can write information to and log.

User · Answer

Just as a notice  I made a test function for my spreadsheet  I use the variable google throws in the onEdit e  function  I called it e   Then I made a test function like this   function test    var testRange   SpreadsheetApp getActiveSpreadsheet   getSheetByName GetItemInfoSheetName  getRange 2 7  var testObject         range testRange      value  someValue    onEdit testObject  SpreadsheetApp getActiveSpreadsheet   getSheetByName GetItemInfoSheetName  getRange 2 6  setValue Logger getLog        Calling this test function makes all the code run as you had an event in the spreadsheet  I just put in the possision of the cell i edited whitch gave me an unexpected result  setting value as the value i put into the cell   OBS  for more variables googles gives to the function go here  https   developers google com apps-script guides triggers events google sheets events

User · Answer

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

User · Answer

2017 Update  Stackdriver Logging is now available for Google Apps Script  From the menu bar in the script editor  goto  View  gt  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

User · Answer

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

User · Answer

A little hacky  but I created an array called  console   and anytime I wanted to output to console I pushed to the array  Then whenever I wanted to see the actual output  I just returned console instead of whatever I was returning before         return  console    uncomment to output console     return  actual output

User · Answer

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

User · Answer

The dev console will log errors thrown by the app script  so you can just throw an error to get it logged as a normal console log  It will stop execution  but it might still be useful for step by step debugging   throw Error  hello world       will show up in the console similarly to console log  hello world

User · Answer

UPDATE       As written in this answer        Stackdriver Logging is the preferred method of logging now      Use console log   to log to Stackdriver      Logger log will either send you an email  eventually  of errors that have happened in your scripts  or  if you are running things from the Script Editor  you can view the log from the last run function by going to View- gt Logs  still in script editor   Again  that will only show you anything that was logged from the last function you ran from inside Script Editor   The script I was trying to get working had to do with spreadsheets - I made a spreadsheet todo-checklist type thing that sorted items by priorities and such   The only triggers I installed for that script were the onOpen and onEdit triggers  Debugging the onEdit trigger was the hardest one to figure out  because I kept thinking that if I set a breakpoint in my onEdit function  opened the spreadsheet  edited a cell  that my breakpoint would be triggered  This is not the case   To simulate having edited a cell  I did end up having to do something in the actual spreadsheet though  All I did was make sure the cell that I wanted it to treat as  edited  was selected  then in Script Editor  I would go to Run- gt onEdit  Then my breakpoint would be hit   However  I did have to stop using the event argument that gets passed into the onEdit function - you can t simulate that by doing Run- gt onEdit  Any info I needed from the spreadsheet  like which cell was selected  etc  I had to figure out manually   Anyways  long answer  but I figured it out eventually     EDIT   If you want to see the todo checklist I made  you can check it out here   yes  I know anybody can edit it - that s the point of sharing it    I was hoping it d let you see the script as well  Since you can t see it there  here it is   function onOpen       setCheckboxes        function setCheckboxes       var checklist   SpreadsheetApp getActiveSpreadsheet   getSheetByName  checklist      var checklist data range   checklist getDataRange      var checklist num rows   checklist data range getNumRows      Logger log  checklist num rows      checklist num rows      var coredata   SpreadsheetApp getActiveSpreadsheet   getSheetByName  core data      var coredata data range   coredata getDataRange       for var i   0   i  lt  checklist num rows-1  i          var split   checklist data range getCell i 2  3  getValue   split              var item id   split split length - 1       if item id                item id   parseInt item id         Logger log  setting value at     i 2    2  to     coredata data range getCell item id 1  3  getValue           checklist data range getCell i 2 2  setValue coredata data range getCell item id 1  3  getValue                  function onEdit       Logger log  TESTING TESTING ON EDIT      var active sheet   SpreadsheetApp getActiveSheet      if active sheet getName       checklist         var active range   SpreadsheetApp getActiveSheet   getActiveRange        Logger log  active range      active range       Logger log  active range col      active range getColumn      active range row      active range getRow         Logger log  active range value      active range getCell 1  1  getValue         Logger log  active range  colidx      active range getColumnIndex         if active range getCell 1 1  getValue             active range getCell 1 1  getValue                   Logger log  made it           var next cell   active sheet getRange active range getRow    active range getColumn   1  1  1  getCell 1 1         var val   next cell getValue          Logger log  val      val         var splits   val split                var item id   splits splits length-1         Logger log  item id      item id          var core data   SpreadsheetApp getActiveSpreadsheet   getSheetByName  core data          var sheet data range   core data getDataRange          var num rows   sheet data range getNumRows          var sheet values   sheet data range getValues          Logger log  num rows      num rows          for var i   0  i  lt  num rows  i              Logger log  sheet values      i            8             sheet values i  8            if sheet values i  8     item id              Logger log  found it  tyring to set it                 sheet data range getCell i 1  2 1  setValue active range getCell 1 1  getValue                                     setCheckboxes

User · Answer

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    Use console log  Hello World   in your script  Go to https   script google com home my and select your add-on  Click on the ellipsis menu on Project Details  select Executions       Click on the header of the latest execution and read the log

User · Answer

just debug your spreadsheet code like this       throw whatAmI        shows like this

User · Answer

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

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

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