You don't say anything about what environment you are working with and I would guess you're not working with a server-side environment. JavaScript normally works in a browser to respond to the user's clicks and mouse moves etc but strictly within the confines of the browser. What you are trying to do is perform I/O operations on the underlying OS that the browser is running in (if you are running locally) or on the server-side OS in a normal webpage environment. It's not just a security issue - JavaScript simply doesn't have any direct connection to the client's OS or the server-side OS for that matter.
What you need is a web server environment like Apache or IIS etc, probably running an environment like ASP.NET, JSP, PHP(with a nice framework like CodeIgniter), or, rather you than me, CGI.
The user clicks a link or a submit button, and sends a request to the server. The relevant server-side program processes the request, runs the I/O operation you talk about and responds with the text. JavaScript is irrelevant in most of that process. It only comes into its own again when you are trying to figure out how to display the response in some fancy dynamic way.
There are millions of tutorials out there:
Having said all that, there is a server-side JavaScript environment (http://nodejs.org/) but the point is you will always be restricted by the limitations of the http protocol which means that you send a request to a server, the server processes your request depending on your privileges as a client, performing an I/O operation if appropriate, and responds with a stream of HTML. It does not allow direct operations on the server.
None of this is easy. Expect steep learning curves.
Displaying the text file contents
Here's a sample JSP page which will read the contents of a text file then display it on the webpage. I haven't added any buttons or anything - it just demonstrates how to read a file on the server:
<%@page contentType="text/html" pageEncoding="UTF-8" import="java.io.*"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>BufferedReader</title>
</head>
<body>
<%
String path = this.getServletContext().getRealPath("/target/message.txt");
File file = new File(path);
FileReader reader = new FileReader(file);
BufferedReader br = new BufferedReader(reader);
while(br.ready()){
out.print(br.readLine() + "<BR>");
}
reader.close();
%>
</body>
</html>
/target/message.txt is the virtual absolute path (from the root of the webapp). The call to getRealPath is the way you get a real physical path that allows you to create a File object.
I'll have a look later at using exec to run a batch file, but now you're thinking of a powerful language/library like Java why do you want to run a batch file? Wouldn't it make sense to write the program in Java?
