Ten days to implement the [Javascript] lexer, parser, bytecode emitter (which I folded into the parser; required some code buffering to reorder things like the for(;;) loop head parts and body), interpreter, built-in classes, and decompiler... Ten days without much sleep to build JS from scratch, "make it look like Java" (I made it look like C), and smuggle in its saving graces: first class functions (closures came later but were part of the plan), Self-ish prototypes (one per instance, not many as in Self).
That's from Brendan Eich, the guy who created Javascript. Guess you never know when your 10 day project might go big and become something like the assembly for the web. Release early and iterate often seems to hold up quite well here....