How do I read a file into a JavaScript variable?

Ans:)Reading a file from JavaScript is (almost) as easy as reading a file from a
Java applet. Your script cannot read files itself;you would have to code a Java
applet that reads files for your script.

In more detail, one of the possible reading mechanisms can work like this:

Your script calls a public method of the applet.

1. The public method initiates the reading process in another thread of the
   applet, and then returns.
2. The reading process in another thread of the applet continues. At the same
   time, the script keeps asking the applet whether the reading is complete.
3. The applet finishes reading and puts the file content in a public string
   variable of the applet.
4. The script sees that the applet completed reading.
5. The script copies the file content from the applet's public variable into a
   Javascript variable.

Note that unsigned Java/JavaScript code can read files only if the file(s) to
read and the code itself have the same origin. For example, if your unsigned code is published on a Web server, it is allowed to read files from the same server only. If your code resides on the local hard disk,it is allowed to read files only from the
same disk (at best).

Ans:) Writing a file from JavaScript is just as easy as writing a file from a Java applet. Your script cannot write files itself; it should call a Java applet's public method which will actually do all the dirty file writing work for you.

The bad news is that

1. Writing is a privileged operation, and therefore your Java applet must be
   digitally signed in order to write files.
2. Applet signing for Internet Explorer is completely different from applet signing for Netscape Navigator.
3. Signed applets may not work properly in Netscape Navigator 3.
4. What's the worst, it's very insecure to put privileged operations in public
   methods of signed applets! If you publsh such an applet, a malicious code could
   easily subvert the applet's public methods, and you (the applet publisher/signer)
   will be sued for any damage!

Therefore, nobody publishes scripts that write files via signed applets, although in versions 4 of both major browsers it's technically possible.

Ans:) JavaScript is supported by the following browsers:

• Netscape Navigator (beginning with version 2.0)
• Microsoft Internet Explorer (beginning with version 3.0)
• Any other browser/product whose vendor licensed or implemented JavaScript
  interpreter (for example, Opera).

Ans:)JavaScript is one of the youngest programming languages. It was first
implemented by Netscape Communications in 1995.The first browser to support
JavaScript was Netscape Navigator 2.0 beta version. By 1999 the two major
browsers,Netscape Navigator and Microsoft Internet Explorer,supported the following
client-side versions of JavaScript:.

Browser javaScript Version	Year
Netscape Navigator 2.0 JavaScript 1.0	1995
Microsoft Internet Explorer 3.0 JavaScript 1.0 (JScript 1.0)	1996
Netscape Navigator 3.0 JavaScript 1.1	1996
Netscape Navigator 4.0 JavaScript 1.2	1997
Microsoft Internet Explorer 4.0 JavaScript 1.2 (JScript 3.0)	1997
Netscape Navigator 4.5 JavaScript 1.3	1998
Microsoft Internet Explorer 5.0 JavaScript 1.3 (JScript 5.0)	1999