JavaScript Limitations

JavaScript FAQ | Basic Syntax & General Questions

Question: What can't JavaScript programs do?

Answer: JavaScript code cannot do any of the following:

use printers or other devices on the user's system or the client-side LAN
(For a workaround, see Printing JavaScript output.)
directly access files on the user's system or the client-side LAN; one notable exception is the access to cookie files.
(For additional discussion of file input/output, see the File Access section.)
implement multiprocessing or multithreading.

If you do need to access files or perform other "privileged" operations, you can use JavaScript in combination with a Java applet. Signed Java applets are allowed to do "privileged" things, and your JavaScript programs can exchange information with applets. However, you have to bear in mind the biggest JavaScript/Java limitation: the user can always disable Java or JavaScript or both!