test.js

var foo = function(text, callback) {
  if(text == "hello") {
    callback("hello world");
    console.log("Someone said hello");
  }
  callback("why don't you say hello?");
  console.log("nobody likes me :(");
}

foo("hello", function(result) {
  console.log(result)
});

foo("asdasdasd", function(result) {
  console.log(result)
});