JavaScript was first developed for use in web browsers. Its input and output capabilities in that context are somewhat limited, this mainly being due to the security considerations of allowing a third party to run a script on your computer.

In a web browser implementation, the I/O is limited to being able to access form data, the inner text or HTML of document objects, or perform document writes.

When JavaScript is used server-side, or as a general purpose scripting language for automation, then the implementation adds much more sophisticated I/O capabilities. For example, ScriptEase adds many file and stream based I/O capabilities found in the C language.

Cross-references:

Wrox Instant JavaScript - page - 13