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Javascript trigger download outside of browser

What would be the best way of triggering a download outside of the browser?
I have a Html Page which is not on a Server but should only function as a Digital Signage Viewer. The Server (which already exists) sends a playlist over TCP Sockets (the server is a bit older) telling the client what media it needs to download from where and where the media is supposed to be presented.
The communication between the Javascript Client code and the Tomcat server is irrelevant for now. What I would like to know is if there is a way to download the files to a certain directory without letting the browser download the file (Problems -> Download Pop Up -> Confirmation -> Can't preset different download folders etc. with Javascript), so that I can set the source of the media tags after they have downloaded ?
(If you're asking why I'm not simply streaming the media it's because if the connection is lost the media still needs to continue to play)
I really hope my explanation makes any sense.
Cheers
Cris

You may send the content to a web server and return it back to browser with specified type/filename. For example in PHP you may do something like this:
header('Content-type: text/html');
header('Content-disposition: attachment;filename=myfile.txt');
Another option is this nice JavaaScript library which allows you to save some contents on client-side:
https://github.com/koffsyrup/FileSaver.js
It allows you to do something like this in browser:
saveTextAs("Hi,This,is,a,CSV,File", "test.csv");
You may also want to store your contents in browser's localStorage or sessionStorage.

What I would like to know is if there is a way to download the files to a certain directory without letting the browser download the file
If this would be possible it would open a security leak because it would make it possible to put special files (like programs) into special folders (like autostart) and then cause unwanted execution of code. This this is hopefully not possible due to security concerns.

Read local file content and send it to server using Javascript

I am writing a very simple Elearning application for my virtual class. I wander if there may be a way using Javascript that works on the background to read the content of a file located on the user's computer and send its content to my server. Any one knows an open source code of Javascript doing this ?
I think that this can be done using XMLHttpRequest, i.e. AJAX, but I could not graps my way through. Any help

You can't gain access to a local file in browser because you are in sandbox, but there are some File API for Html 5 that you can programmatically select them and access their data just have a look at the following link
File API
Web applications should have the ability to manipulate as wide as possible a range of user input, including files that a user may wish to upload to a remote server or manipulate inside a rich web application. This specification defines the basic representations for files, lists of files, errors raised by access to files, and programmatic ways to read files. Additionally, this specification also defines an interface that represents "raw data" which can be asynchronously processed on the main thread of conforming user agents. The interfaces and API defined in this specification can be used with other interfaces and APIs exposed to the web platform.

Unfortunately there is no way to give JavaScript any access to the user's local files.
There is a very serious security issue with that.
There is however API for that on IE browsers (Which give nice big warning when you attempt to access the files)
I recommend to ask from the user to upload his own file (using <input type="file" />) and upload it to the server.

HTML5 specifications specify an API to access the local filesystem. It is supported in the latest versions of Chrome. See here for details http://net.tutsplus.com/tutorials/html-css-techniques/toying-with-the-html5-filesystem-api/.
If the environment is controlled (i.e in a classroom or intranet) you can build your application using this API.

Is it possible to upload and extract a zip file to a given location using only HTML and JavaScript?

I have a web page which asks users to select a zip file on their machine and upload it. It also asks for a destination on the server where the zip file should go. I want it to work in such a way that when they tell me where the file is on their machine and where it belongs on my server, then click "send," it should be sent to my server, placed in the designated directory, and unzipped.
I want to do this in just HTML and JavaScript. Is that possible? If so, how would I go about doing it?

You have to do this serverside; the client's browser cannot write to the file system of the server directly as it's a huge security risk.
In addition to that, not even HTML5 with it's File API can extract ZIP files. You need to do it on the server with PHP, or whatever language you're using.
If you just want to do things locally on the client, you could consider a Flash/Java/Browser extension, but I wouldn't recommend it for compatibility and performance reasons. Your best bet is to send a request to the server for it to process and send back. You're already serving the HTML page, so you can use the same server to process the ZIP file.
If, on the other hand, you want to write the ZIP file to the server, you have to do it server side for reasons stated in my first paragraph.

You can unzip/zip content within JavaScript using rawdeflate.
As other posters suggest, you cannot save directly to the local filesystem using a plain browser. You either need to echo the result back off the server (in which case it may as well unzip), or you can use Flash, for example, Downloadify, if it is installed.
Most modern browsers support FileAPI for loading from the local filesystem, certainly, Chrome, Firefox and Opera do. I haven't tested IE 9.

Is it possible to "upload" a file only with client side ? (no server involved)

I am trying to do a simple thing:
Let the user choose a txt file, and save its context to be used on the client side only.
no server side needed.
Is it possible ?
Thanks.

It is possible to do so with HTML5 Files API as explained in these resources:
https://developer.mozilla.org/en-US/docs/Using_files_from_web_applications
http://www.html5rocks.com/en/tutorials/file/dndfiles/

I guess you mean "save its content" and conclude you want to do anything with this content on the client side, e.g. extract some parts to fill a form. Anyway saving the whole file unchanged, on the same machine where it comes from, does not make sense.
So the problem is not how to upload, but how to open/read a file. You can do this with a Java Applet, Flash, Silverlight, ActiveX ... just to name a few.
JavaScript is not an option. It cannot access the file system.

If the html page, that is hosting your javascript, is from a remote server. This script is not trusted to do actions on your local filesystem.
<Obscure solution mode level = 1>
You can give more trust to a page, but this is something your user has to do. If this is an app/web only for use within an enterprise, you can probably do this centrally. And every browser handles this differently. So it is not something you can rely on, when you do not have a limited userbase.
<Obscure solution mode level = high>
If your (enterprise) users are using Internet Explorer, you could also create a HTML Application (simply give your html page an hta extension). These pages have full trust, but can only be started from a trusted location, or require confirmation from the user.

The only way you can acheive this successfully is to build an ActiveX type plugin/component (or java applet) you will have much more control of the client machine.

No. JavaScript cannot access the local filesystem.
However, you could install a webserver on your machine and e.g. run PHP on that one. Then you could do it without ever sending your data over a network connection. That would require you to do your data processing in PHP though.. probably not what you want. Or you could simply send back the data to your javascript.. but that'd be pretty awful to run an upload just to make the data available to JavaScript.

Upload a file to an html page with no backend?

Is it possible to read the contents of an uploaded file (through <form><input type="file">) from inside javascript with no backend? I suppose it's possible with HTML5, but what about HTML4?

You can read (not upload - well, you can upload too, but that's like sending fan-mail to Edgar Allen Poe; nothing stops you but he won't be able to read it) from files if your script runs in a very trusted context.
If anyone on your network is browsing the web in a browser set to give that much trust, disconnect their machine from the network first, make their settings tighter second.

I don't know if I understand correctly. How about using something like uploadify together with jQuery. I guess you'll have to grant the webserver the privilege to write in the specified folders.

The security model will not let you unless you change the security to allow this.
http://www.mozilla.org/projects/security/components/signed-scripts.html
Can you elaborate on what you want to do?
I read the question as "How do I grab the contents from a file chosen using a file upload field and process it on the client without involving a backend/webserver".
I am thinking UniversalBrowserRead access for FF and HTA filesystem for IE for example