Why is this variable sometimes undefined?

Question

So this function gets a folder, gets the subfolders, pushes some information to an array and then pastes the array into my spreadsheet.

It fails at a weird point about 2-5% of the time, and the attempts I have made to error catch it earlier just don't work. why/how!

function getFileCount(gdrive,level,fullpath){
  var folder = DriveApp.getFolderById(gdrive);
  var fileCount = 0;


  //append the subfolders to the sheet 
  var folders = folder.getFolders();
  var result = [];
  while (folders.hasNext()){
    var folder = folders.next();
    var path = fullpath + " > " +folder.getName();
    result.push([(level+1),folder.getId(), path,"?"]);
  }
  if (result == []) return fileCount;
  if (result == undefined) {console.log("Why the hell is it undefined?"+folder.getName()); return fileCount;}
  var sh = SpreadsheetApp.getActiveSpreadsheet();
  var ss = sh.getSheetByName("FoldersPlusCounts");
  var end = ss.getLastRow()+1;  
  try{ss.getRange(end, 1,result.length, result[0].length).setValues(result);}catch(e){console.log(e+" "+gdrive+" ["+result+"]");return -1;}
  if (result.length > 0) SpreadsheetApp.flush();

  return fileCount;
}

the try catch statement is where it fails saying:

TypeError: Cannot read property 'length' of undefined 1dmDV2qdnU2Qqrg6mr-sxD8JaQncTUNqn []

This doesn't occur every time the folder has no files, or every time it has no folders, I don't think.

So how can result sometimes be undefined, when it is clearly defined as result = [], and if it is undefined, why isn't it being captured by the "if result == undefined" line?

Some lines removed for clarity (just the file counting stuff), I wasn't using result up in that part anyway.

Your error probably stems from the 4th argument that you pass to your `getRange()` ie. `result[0].length`. It could be that the 0th element in your `result` array does not have a `length` property. — TheAddonDepot, Oct 30 '19 at 21:04
Ok, I thought to check the length of the array in general and that seeems to be fixing my problem. Why doesn't if (result == []) work? — J. G., Oct 30 '19 at 21:10
In your script, it's `var result = [];`. And `result` is compared with `[]`. At Javascript, in this case, the object is compared as the reference. By this, `result == []` is always `false`. When you want to confirm whether `result` is `[]`, how about modifying to `result.length == 0`? — Tanaike, Oct 30 '19 at 22:11
You have two declarations for `folder`. `var folder=DriveApp.getFolderById(gdrive);//here var fileCount=0; var folders=folder.getFolders(); var result=[]; while (folders.hasNext()){ var folder = folders.next();//and here` — Cooper, Oct 30 '19 at 22:41
yes, changing to check for result.length == 0 fixed it for me, Tanaike I didn't know that (result == []) will always be false — J. G., Oct 30 '19 at 23:00
Tanaike can you make your answer the answer? I'm sure coopers works as well but yours was the change that fixed it. — J. G., Oct 30 '19 at 23:17
Thank you for replying. I posted an answer. Could you please confirm it? — Tanaike, Oct 30 '19 at 23:32

Tanaike · Accepted Answer · 2019-10-30T23:37:55.487

In your script, result is declared as var result = [];. And result is compared with [].

At Javascript, in this case, the object is compared as the reference. By this, result == [] is always false. In order to confirm whether result is [] which is empty, how about the following modification?

From:

result == []

To:

result.length == 0

or

!result.length

References:

Array.length
How to compare arrays in JavaScript?
- I think that also this thread might help for understanding this situation.

score 0 · Answer 2 · answered Oct 30 '19 at 22:58

This worked for me:

function getFolderCount(){
  var fldr=DriveApp.getFolderById('folderId');
  var subfldrCount=0;
  var subfolders=fldr.getFolders();
  var result=[];
  while (subfolders.hasNext()){
    var subfolder=subfolders.next();
    result.push([++subfldrCount,subfolder.getName(),subfolder.getId()]);
  }
  var ss=SpreadsheetApp.getActive();
  var sh=ss.getSheetByName("FoldersPlusCounts");
  sh.getRange(sh.getLastRow()+1, 1,result.length, result[0].length).setValues(result);
}

Why is this variable sometimes undefined?

2 Answers2

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