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].