Can javascript access a filesystem?

I was pretty sure the answer was NO, and hence google gears, adobe AIR, etc.

If I was right, then how does http://tiddlywiki.com work? It is persistent and written in javascript. It is also just a single HTML file that has no external (serverside) dependencies. WTF? Where/how does it store its state?

Tiddlywiki has several methods of saving data, depending on which browser is used. As you could see in the source.

• If ActiveX is enabled, it uses Scripting.FileSystemObject.
• On Gecko-based browsers, it tries to use UniversalXPConnect.
• If Java is enabled, it uses the TiddlySaver Java applet.
• If Java LiveConnect is enabled, it tries to use Java's file classes.