cb.js

var caller = function(val, cb) {
  var result = cb(val);
  if (result == 1) {
    return true;
  }
  else {
    console.log("Invalid response " + result);
  }
  console.log("I'm never shown if result == 1");
}

caller(1, function (v) { return v * 1; });
// returns true

caller(1, function (v) { return v * 2; });
// returns undefined (fal'cie)