Write a file with Prototype or plain Javascript

I know the question has been asked thousands of times, but I'll ask it again: is there a way (even patch开发者_StackOverflow中文版y) to write/read a dumb text file with Javascript or Protoype ?

This is only for debug purposes, and is not designed for production. The thing is I need it to work with (at least) both Firefox and IE (preferably under Windows).

Thanks in advance !

Writing to a file is not possible, you'd have to write a server-side script and make a request to that script. Reading is possible if you use an iframe with the text file's location as source, and reading the iframe contents.

It is possible to read/write to a local file via JavaScript: take a look at TiddlyWIki. (Caveat: only works for local documents.)

I have actually written a Single Page Application (SPA) using twFile, a part of the TiddlyWiki codebase:

1. Works in different browsers: (IE, Firefox, Chrome)
2. This code is a little old now. TiddlyWiki abandoned the jQuery plugin design a while ago. (Look at the current TiddlyWiki filesystem.js for more a more recent implementation. It's not isolated for you like the twFile plug-in, though).
3. Although written as a jQuery plug-in, I've studied the code and it is almost completely decoupled from jQuery.

Update: I have uploaded a proof-of-concept that accesses a local file via JavaScript.

• Modifying this application to write to a file is trivial.
• I have not tried to get this to work as a file served from a web server, but it should be possible since there are server-side implementations of TiddlyWiki<>.

Update:

So it looks like the server side implementations of TiddlyWiki use a server "adapter" to modify a file stored on the server, similar to Peter's description. The pure JavaScript method will probably not work if the page is served from a web server due to cross-domain security limitations.

Javascript in browsers doesn't allow you to write local files, for security reasons. This may change with time, but as for now you have to deal with it.

Only with a server side javascript interpreter, but that isn't the typical environment you run javascript in.

What about cookies? It is accessible via javascript, it is on your client and it is a plain text file. Only issue is the size of it (4k max if I remember well).

What you can do as well is use your browser localStorage / userData / globalStorage (depending on your browser version). It acts like cookies (new webStorage / HTML5 specs) but can handle bigger amounts of data. Then, using some add ons (firebug on firefox for instance) you can easily read / copy / past the value and do whatever you have to do with it!