Animate CC AS3 how to manage data when writing to a file - actionscript-3

Question

I am building a program on Animate CC 2019 which needs to access a text file where it can read from and write to.
I want to store strings and numbers, from Input Texts, then write them in the file, in addition to the already existent contents.
I also need to be able to manage how the data is written in the file. So, for example, I want to have 2 arrays: Array1 stores names and Array2 stores numbers. So when the program writes to the file, it needs to write on each line the corresponding values of a specific index in the arrays. So if Array1(0) = name1 & Array2(0) = 52, in the file it should be written:
name1 52
If not exactly like this, a way which data can be written in a manageable way.
I am trying this on Windows 10/AIR.
My questions:
How can I manage how data are written in a file?
Which code should I use? I find info on two ways to approach this:
a. Code using “File” and “FileStream” which does NOT work! I get error messages: “Type was not found or was not a compile-time constant” for both, like the system does not recognize the commands. Are these commands still usable on the current version of Animate CC?
b. The code snipets/AIR code which does work, however, I cannot find a way to manage how data are written in the file, as explained above. Everytime something is written in the file, the previous data are overwritten.
Below the codesnipets code which works.
/* Click to Write to a Text File
Clicking on the specified object will prompt the user to select a location and file name and save a text string to it.
Instructions:
To set what data is saved to the file change "Text to save to file." to the data you wish to save.
*/
import flash.filesystem.File;
import flash.filesystem.FileMode;
import flash.filesystem.FileStream;
movieClip_1.addEventListener(MouseEvent.CLICK, fl_SaveFile);
var fl_FileDataToSave:String = "Text to save to file.";
var fl_SaveFileStream:FileStream = new FileStream(); // FileStream used to write to the file
var fl_SaveFileChooser:File = File.documentsDirectory; // Default to the documents directory
fl_SaveFileChooser.addEventListener(Event.SELECT, fl_WriteFileHandler);
// Opens a Save As dialog box for user to specify a file name
function fl_SaveFile(event:MouseEvent):void
{
fl_SaveFileChooser.browseForSave("Save As:");
}
// Write data in fl_FileDataToSave variable
function fl_WriteFileHandler(event:Event):void
{
fl_SaveFileChooser = event.target as File;
fl_SaveFileStream = new FileStream();
fl_SaveFileStream.openAsync(fl_SaveFileChooser, FileMode.WRITE);
fl_SaveFileStream.writeMultiByte(fl_FileDataToSave, File.systemCharset);
fl_SaveFileStream.close();
}