Real use-case for the advanced "fun.length" feature of JavaScript

lazy.js

function bindSomething (cb) {
  anyEventSystem.on("something", function (e) {
    if (cb.length === 0) {
      cb();
    }
    else {
      var computation = takesALotOfCPU();
      cb(computation);
    }
  });
}


bindSomething(function (computation) {
  console.log("something!", computation);
});

bindSomething(function () { // Nothing !
  console.log("something!");
});