The && and || operators use short-circuit logic, which means they will execute their second operand dependant on the first. This is useful for checking for null objects before accessing their attributes: var name = o && o.getName();Or for setting default values: var name = otherName || "default"; http://simon.incutio.com/slides/2006/etech/javascript/js-reintroduction-notes.html#overview several js app(one page , one application) http://trimpath.com/demos/nextaction_static1/nextaction.htm http://trimpath.com/project/wiki/NextAction