Date: 2009jul26 Language: javaScript Q. How do I get warnings about undeclared variables in javaScript? A. In Firefox, go to

about:config

And set

javascript.options.strict = true

This is like perl's "use strict;". It also, helpfully, warns about variables with overlaping scope. Since this generates lots of warning from things I don't control (eg jQuery). I prefer to just turn it on occasionally.