Luckily thanks to jQuery, my productivity with this language is much better!
Using this website to test code is great, especially combined with FireBug (extension for debugging) for code problems. The following example is a function to determine if the postal code of Spain (typically 4 or 5 digits) is correct with respect to the province (the postal code is usually PPXXX where PP is the code of the province, and XXX is assigned) .
As you can see, I have caused an error in this code that you can discover thanks to FireBug, so … my experience is pretty good, besides being an online tool, and I can see the result with document.write(valor).
JSFiddle, another cool alternative