from-promise.js

// Submit the form when the submit button is clicked
var signUpCommand = function(emailAddress) {
  var promise = $.ajax({
    type: 'POST',
    url: '...',
    data: JSON.stringify({
      'email': emailAddress
    }),
    contentType: 'application/json; charset=utf-8',
    dataType: 'json'
  }).promise();
 
  return Rx.Observable.fromPromise(promise);
};
 
var submitButtonClickedSignal = Rx.Observable.fromEvent($submit, 'click');
 
var submissionSignal = submitButtonClickedSignal
  .flatMapLatest(function(e) {
    return signUpCommand($input.val());
  });
 
submissionSignal
  .subscribe(function(data) {
    console.log(data);
  }, function(error) {
    console.error(error);
  }, function() {
    // This never gets called
    console.log('onCompleted');
  });