JSLint

JSLint is a code quality tool for JavaScript which checks your syntax.

Having read through this appendix (you can read more about JSLint here), I tend more towards JSHint, a fork of JSLint. It allows programmers to customise for themselves which the good parts and bad parts are and define their own subset, although naturally there are a number of pre-defined options. This is a really fantastic article on using JSHint; it's simple and aimed at having you using JSHint in a few minutes as well as providing various sources for pre-defined subsets.

Interesting article on prototypes: http://sporto.github.io/blog/2013/02/22/a-plain-english-guide-to-javascript-prototypes/