Puzzles

    doSomething().then(function () {
      return doSomethingElse();
    });

    doSomething().then(function () {
      doSomethingElse();
    });

    doSomething().then(doSomethingElse());

    doSomething().then(doSomethingElse);

Here is the answer to each one, in graphical format so you can better visualize it:

doSomething().then(function () {
  return doSomethingElse();
}).then(finalHandler);

Answer:

doSomething
|-----------------|
                  doSomethingElse(undefined)
                  |------------------|
                                     finalHandler(resultOfDoSomethingElse)
                                     |------------------|
    

doSomething().then(function () {
  doSomethingElse();
}).then(finalHandler);

Answer:

doSomething
|-----------------|
                  doSomethingElse(undefined)
                  |------------------|
                  finalHandler(undefined)
                  |------------------|
    

doSomething().then(doSomethingElse())
  .then(finalHandler);

Answer:

doSomething
|-----------------|
doSomethingElse(undefined)
|---------------------------------|
                  finalHandler(resultOfDoSomething)
                  |------------------|
    

doSomething().then(doSomethingElse)
  .then(finalHandler);

Answer:

doSomething
|-----------------|
                  doSomethingElse(resultOfDoSomething)
                  |------------------|
                                     finalHandler(resultOfDoSomethingElse)
                                     |------------------|