How to convert all comments to notes using appsscript in googlesheets?

I want to get all the comments in google sheet cells to convert as a note in the same cell. Here the data in the cell should not change. And the name of the person who made the comment should also be included.
I used this code for the first requirement. But it didn't work. How can this be done correctly?

function convertCommentsToNotes() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var range = sheet.getDataRange();
  var notes = range.getNotes();

  for (var i = 0; i < notes.length; i++) {
    for (var j = 0; j < notes[i].length; j++) {
      var note = notes[i][j];
      var comment = sheet.getRange(i + 1, j + 1).getComment();
      if (comment !== null) {
        var commentText = comment.getRange().getValue();
        note = note + "\n\n" + commentText;
      }
      sheet.getRange(i + 1, j + 1).setNote(note);
    }
  }
}

I believe your goal is as follows.

• You want to convert the comments to cells as the notes to the same cells using Google Apps Script.
• You want to add the comments to the existing notes.

Issue and workaround:

In the current stage, in order to retrieve the comments from Spreadsheet, Comments of Drive API is required to be used. But, even when the comments are retrieved from the API, it is like "anchor": "{\"type\":\"workbook-range\",\"uid\":0,\"range\":\"123456789\"}" while the comment text can be obtained. Unfortunately, it cannot be known the anchor cell from \"range\":\"123456789\".

From the above situation, I created a Google Apps Script library for obtaining the comments from the cells. Ref In this answer, I would like to propose a modified script for reflecting this library.

Usage:

1. Install Google Apps Script library.

You can see how to install it at here.

2. Enable Drive API.

Please enable Drive API at Advanced Google services. Ref

2. Sample script.

Please copy and paste the following script to the script editor of Spreadsheet.

function convertCommentsToNotes() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const ssId = ss.getId();
  const sheet = ss.getActiveSheet();
  const notes = sheet.getDataRange().getNotes();
  const res = DocsServiceApp.openBySpreadsheetId(ssId).getSheetByName(sheet.getSheetName()).getComments();
  const obj = res.reduce((o, { range, comment }) => (o[`${range.row - 1}_${range.col - 1}`] = comment.map(e => e.comment.trim()).join("\n"), o), {});
  const maxRows = sheet.getMaxRows();
  const maxCols = sheet.getMaxColumns();
  const newNotes = [];
  for (let i = 0; i < maxRows; i++) {
    const temp = [];
    for (let j = 0; j < maxCols; j++) {
      const note = ((notes[i] && notes[i][j]) ? notes[i][j] : "") + (obj[`${i}_${j}`] || "");
      temp.push(note);
    }
    newNotes.push(temp);
  }
  sheet.getRange(1, 1, newNotes.length, newNotes[0].length).setNotes(newNotes);

  // If you want to delete all comments, you can also use the following script.
  // But, when you use the following script, please be careful about this, because all comments are deleted.
  // const commentIds = Drive.Comments.list(ssId).items.map(({ commentId }) => commentId);
  // commentIds.forEach(id => Drive.Comments.remove(ssId, id));
}

• When this script is run, all comments in the active sheet of Google Spreadsheet are retrieved. And, those comments are added to the existing notes.

Reference:

• DocsServiceApp (Author: me)