Access Local Files with Local Javascript [duplicate]

Question

Based on the other answers on this site, I already feel like I know the answer to this question, but, as it's slightly different, I wanted to ask.

Is it possible to access local files from JavaScript that is running locally on the machine (AKA, my website address will be file:///C:/...)? Or, is this sandboxed as well?

What I am trying to do: I have a standalone computer that I want people to be able to drop in JSON or XML files into a local folder which are read in at the creation of the site and used to generate a single web page. If the JavaScript solution is not possible, can you provide any other suggestions?

Thank you.

Answer 1

A webpage can read any file on the same server as it was loaded from (this is the cross-site policy of JavaScript). That means that the page file:///C:/mywebsite/index.html can read the file file://C:/somedir/somefile.xml. To read this file, either use ajax, load it in an iFrame or load it as a javascript or css file.

Several browsers support custom methods for loading local file (and other interesting things), IE has activeX and Firefox has XPCOM.

Answer 2

According to the Firefox documentation, the following code will work:

var req = new XMLHttpRequest();  
req.open('GET', 'file:///home/user/file.json', false);   
req.send(null);  
if(req.status == 0)  
  dump(req.responseText);

I seem to recall it only works within the same directory as the HTML page. And I don't know if this will work in other browsers.

Answer 3

This will only work on IE, but if that is not a problem for you, here is some sample code to write to a file:

    var fso, s;
    fso = new ActiveXObject("Scripting.FileSystemObject");
    s = fso.OpenTextFile("c:\\path\\to\\myfile.txt" , 8, 1, -2);
    s.writeline("Hello World");
    s.Close();

And then to read from it:

f = fso.OpenTextFile(filename, ForReading);
while (!f.AtEndOfStream) {
    var r = f.ReadLine();
    document.write (r + "<br />");
}
f.Close();

For more information about OpenTextFile, check out: http://msdn.microsoft.com/en-us/library/314cz14s(VS.85).aspx