Sometimes when you define an incoming API route, you want it to match certain environment or aspect conditions. The addRoute() has an argument called condition, which can be a closure or UDF pointer that must return a boolean and receives the incoming requestString. You can then decide if the route should execute or just be ignored.

So if a route matches via the pattern, then this closure/UDF is called to verify the route with your own custom conditions. This is a great way to create some routes that must match certain environment criterias before they fire. Let's say you only want to fire some routes if they are using FireFox, or a user is logged in, or whatever.

// condition closure
function(requestString){}

// Routing with condition
addRoute(
    pattern="/go/ff", 
    response="
Hello FireFox!
", 
    condition=function(requestString){
        return ( findnocase( "Firefox", cgi.HTTP_USER_AGENT ) ? true : false );
    }
);