How can we write to local disk (ie on files on the client) using Javascript

I need to save some data from a Chrome Extension either to a local disk file or Google Spreadsheets. The problem I am facing is being able to find a right solution for writing to files using javascript since it is considered to be a security hole and generally not adviced. I need help in figuring on a method to write to local files using Javascript (if it is possible in the fir开发者_如何学编程st place or else please suggest and alternative to this (like any method on how to save data from an extension to Google Spreadsheet).

Thanks in advance

You can't for security reasons. If you could, this would be the ultimate back-door.

You can do this with a signed java applet. [You can also delete/modify/anything user's files].