Open/Save file in javascript

I'll write an app t开发者_运维问答hat'd need to let user load PNG&JSON files and then save them.

How could I let user open and save such files? I wouldn't like to write up an echo server for those images.

You can load files with File API (only supported in firefox 3.6 and chrome unstable (maybe beta) at the moment):

http://dev.w3.org/2006/webapi/FileAPI/

Currently there is no way to save the file

I'll pull Facebook into the conversation. Facebook uses Java to do such a thing.

I should note that you can NOT access the user's hard drive directly in JavaScript. This includes read, write, copy, flag, whatever. It would be a nice security concern, even though most of us who have wanted to do this [including me two years ago] have good intent.

Now, some browsers (cough IE) do allow you to access the user's filesystem through ActiveX, after they click "allow activex"... but that isn't cross-browser/cross-platform, so I wouldn't recommend it. Check: Scripting.FileSystemObject, fopen

You can, however, have the user upload a file to your server, temporarily, load that file client-side, do whatever you want, save the file to the server, and load the image to the user with the mime-header "content" of "application/force-download"...

For security you cannot do it with Javascript alone. The usual ways to access the filesystem from JavaScript require the help of something else:

• Java applets are available on just about all browsers.
• ActiveX is an option on Internet Explorer.
• On Firefox you can use an extension.
• Flash also allows certain kinds of access.

These probably all require some arcane techniques, can be disabled by the user, and may need parts to be specifically installed or OK'd by the user.