From some JavaScript training slides I am working on:

Why use it:

    - Server and client side in the same language
    - Simple enough for you to feel free
    - Enough hammers not to forge your own every time
    - Fast enough
    - Good enough to structure larger programs
    - Browser is the only cross-platform GUI toolkit

When to use it:

    - Web applications
    - Network clients and servers

When not to use it:

    - Computation (CPU) heavy programs
    - Very high loads
    - Shell scripting
    - Raw packet requirement