function CatStrings(p1, p2, p3)

{

  var s = p1;

  if(typeof p2 !== "undefined") {s += p2;}

  if(typeof p3 !== "undefined") {s += p3;}

  return s;

};

​

CatStrings("one");        // result = one

CatStrings("one",2);      // result = one2

CatStrings("one",2,true); // result = one2true

function foo(a, b, opts) {

  // ...

  if (opts['test']) { } //if test param exists, do something.. 

}

​

​

foo(1, 2, {"method":"add"});

foo(3, 4, {"test":"equals", "bar":"tree"});