File API: reader vs.

I have studied many articles and posts to learn about File API and still don’t understand why almost all of them use instead of reader. Here are three examples:

  1. File API
  2. Using files from web applications | MDN
  3. Working with files in JavaScript, Part 2: FileReader | NCZOnline

The last reference even recommends using

The FileReader instance is available inside of the event handler via and it’s recommended to use that instead of referencing the reader variable directly.

But why is it recommended and widely used? What’s wrong with using reader or simpler this instead: DEMO.

I know this and can be different, but in this case they both refer to the FileReader object.

While you can use reader.onload, then why not reader.result?