In Processing.js versions 1.4.7, 1.4.8, and 1.6.6 (but not version 1.4.1) println of a string with a < without white space around it may fail.

See https://jsfiddle.net/blyon/on7a5f9s/ for a simple demo which contains this code :
var a=function(){ return a<a; }; println(a);

A simpler example is println("Strings with a<b don't work.");