function onOpen() {
    var ss = SpreadsheetApp.getActiveSpreadsheet();
    var csvMenuEntries = [{
        name: "export as csv files",
        functionName: "saveAsCSV"
    }];
    ss.addMenu("csv", csvMenuEntries);
};

function saveAsCSV() {
    // gets the destination folder by their ID.
    var folder = DriveApp.getFolderById("1kWASyT9zzN_HtqMDdKr8M64SWDvP0oQR");

    // Get sheet's name
    var sheet = SpreadsheetApp.getActiveSpreadsheet();

    // append ".csv" extension to the sheet name
    var filename = sheet.getName() + ".csv";

    // remove files inside the folder
    var folderId = "1kWASyT9zzN_HtqMDdKr8M64SWDvP0oQR";
    var getfolder = DriveApp.getFolderById(folderId);
    var files = getfolder.getFilesByName(filename);
    if (files.hasNext()) {
        files.next().setTrashed(true);
    }


    // convert all available sheet data to csv format
    var csvFile = convertRangeToCsvFile_(filename, sheet);

    // create a file in the Docs List with the given name and the csv data
    folder.createFile(filename, csvFile);
};

function convertRangeToCsvFile_(csvFileName, sheet) {
    // get available data range in the spreadsheet
    var activeRange = sheet.getDataRange();
    try {
        var data = activeRange.getValues();
        var csvFile = undefined;


        // loop through the data in the range and build a string with the csv data
        if (data.length > 1) {
            var csv = "";
            for (var row = 0; row < data.length; row++) {
                for (var col = 0; col < data[row].length; col++) {
                    if (data[row][col].toString().indexOf(",") != -1) {
                        data[row][col] = "\"" + data[row][col] + "\"";
                    }
                }


                // join each row's columns
                // add a carriage return to end of each row, except for the last one
                if (row < data.length - 1) {
                    csv += data[row].join(",") + "\r\n";
                } else {
                    csv += data[row];
                }
            }
            csvFile = csv;
        }
        return csvFile;
    } catch (err) {
        Logger.log(err);
        Browser.msgBox(err);
    }
};