When you download a file from the MEGA service, you are shown a pretty download progress bar within the browser. Once this progress bar reaches 100%, your browser then begins to download the file. That is, only once the graphical download is complete, your browser's normal download process is started. What exactly is going on here?

1 Answer 1


It uses the fileSystem API, which basically writes the file to a sandboxed section of your local file system:

AppData\Local\Google\Chrome\User Data\Default\File System\

  • 4
    Ah interesting. So the graphical download creates the file in the directory mentioned in your answer. The start of the browser download is the movement from that directory to your download destination folder. Is that right? What are the benefits to this?
    – Jeff
    Mar 4, 2013 at 20:03
  • 6
    Yes, exactly... Well, it seems to copy, not move the file. As for the benefits, i'm struggling to see any! "Resumable" downloads is one, but not being able to choose your download folder isn't ideal. I'm also struggling to find out how long the file is stored in your User Data folder, as i downloaded something from mega about 3 days ago and the 250mb file is still there.
    – Dodswm
    Mar 5, 2013 at 19:41
  • 11
    MEGA works with Firefox which doesn't implement the filesystem API, so I don't think this is the whole answer.
    – Macil
    Oct 17, 2014 at 6:00
  • 4
    File System is just one of the HTML5 persistent storages which can be used to allow download resume. But if resuming is not needed it can just store files in memory, decrypt then and download those using the saveAs() method (or FileSaver.js). Oct 20, 2014 at 11:18
  • 13
    There is only one reason for this: files on mega are encrypted and they stay encrypted until they are on your harddisk. Nov 27, 2014 at 17:07

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