Equivalent of Python's dir in Javascript
The global variables are kept in an easily accessible object (window) and so you can inspect/iterate over them easily. (Using something like the functions suggested by Glenjamin)
On the other hand, I don't know of any way to inspect local variables defined in functions or closures - if this is possible I'd at least guess it would be highly browser/console specific.
when I write Python code from the interpreter I can type dir() to have a list of names defined in the current scope. How can achieve to have the same information, programmatically, when I develop Javascript code from a browser using an interactive console like firebug, chrome console, etc?