Async Operations

/**
 * Creates an observable from a function that uses Node.js callback pattern
 * @param {function} func - Function that takes arguments and a callback(error, result)
 * @param {*} [context] - Context to bind the function to
 * @param {function} [selector] - Function to transform the callback result
 * @returns {function} Function that returns an observable when called with arguments
 */
Rx.Observable.fromCallback = function(func, context, selector);

var fs = require('fs');
var readFile = Rx.Observable.fromCallback(fs.readFile);

var source = readFile('file.txt', 'utf8');
source.subscribe(
  function(data) { console.log('File contents: ' + data); },
  function(err) { console.log('Error: ' + err); }
);

/**
 * Creates an observable from a Node.js-style callback function
 * @param {function} func - Function that takes arguments and a callback(error, ...results)
 * @param {*} [context] - Context to bind the function to
 * @param {function} [selector] - Function to transform the callback results
 * @returns {function} Function that returns an observable when called with arguments
 */
Rx.Observable.fromNodeCallback = function(func, context, selector);

/**
 * Creates an observable from DOM events or EventEmitter events
 * @param {Element|EventEmitter} element - DOM element or EventEmitter
 * @param {string} eventName - Name of the event to listen for
 * @param {function} [selector] - Function to transform the event object
 * @returns {Observable} Observable sequence of events
 */
Rx.Observable.fromEvent = function(element, eventName, selector);

var button = document.getElementById('myButton');
var clicks = Rx.Observable.fromEvent(button, 'click');

clicks.subscribe(function(event) {
  console.log('Button clicked!');
});

/**
 * Creates an observable from a custom event pattern
 * @param {function} addHandler - Function to add event handler
 * @param {function} removeHandler - Function to remove event handler
 * @param {function} [selector] - Function to transform the event arguments
 * @returns {Observable} Observable sequence of events
 */
Rx.Observable.fromEventPattern = function(addHandler, removeHandler, selector);

var source = Rx.Observable.fromEventPattern(
  function(handler) { emitter.addListener('data', handler); },
  function(handler) { emitter.removeListener('data', handler); }
);

/**
 * Creates an observable from a Promise
 * @param {Promise} promise - Promise to convert to observable
 * @returns {Observable} Observable sequence that emits promise result
 */
Rx.Observable.fromPromise = function(promise);

var promise = fetch('/api/data');
var source = Rx.Observable.fromPromise(promise);

source.subscribe(
  function(response) { console.log('Response:', response); },
  function(error) { console.log('Error:', error); }
);

/**
 * Converts the observable sequence to a Promise
 * @param {function} [promiseCtor] - Promise constructor to use
 * @returns {Promise} Promise that resolves with the last emitted value
 */
observable.toPromise = function(promiseCtor);

var source = Rx.Observable.return(42);
var promise = source.toPromise();

promise.then(function(value) {
  console.log('Promise resolved with:', value);
});

/**
 * Creates an observable from a generator function using spawn-like behavior
 * @param {function} generatorFunction - Generator function to execute
 * @returns {Observable} Observable sequence from generator execution
 */
Rx.Observable.spawn = function(generatorFunction);

var source = Rx.Observable.spawn(function* () {
  var a = yield Rx.Observable.return(1);
  var b = yield Rx.Observable.return(2);
  return a + b;
});

/**
 * Invokes a function asynchronously and returns the result as an observable
 * @param {function} func - Function to execute asynchronously
 * @param {*} [context] - Context to bind the function to
 * @param {Scheduler} [scheduler] - Scheduler to execute the function on
 * @returns {Observable} Observable sequence containing the function result
 */
Rx.Observable.start = function(func, context, scheduler);

/**
 * Converts a function to return an observable instead of using callbacks
 * @param {function} func - Function to convert
 * @param {*} [context] - Context to bind the function to
 * @param {Scheduler} [scheduler] - Scheduler to execute on
 * @returns {function} Function that returns an observable
 */
Rx.Observable.toAsync = function(func, context, scheduler);

/**
 * Starts an async function and returns the result as an observable
 * @param {function} functionAsync - Async function that returns a Promise
 * @returns {Observable} Observable sequence containing the async function result
 */
Rx.Observable.startAsync = function(functionAsync);

/**
 * Wraps a function to work with observables
 * @param {function} fn - Function to wrap
 * @returns {function} Wrapped function that works with observables
 */
Rx.Observable.wrap = function(fn);

/**
 * Handles errors from async operations
 * @param {function} handler - Error handling function that returns an observable
 * @returns {Observable} Observable sequence with error handling
 */
observable.catch = function(handler);

/**
 * Retries the async operation on error
 * @param {number} [retryCount] - Number of retry attempts
 * @returns {Observable} Observable sequence with retry logic
 */
observable.retry = function(retryCount);

var source = Rx.Observable.fromPromise(fetch('/api/data'))
  .retry(3)
  .catch(function(error) {
    return Rx.Observable.return({error: 'Failed to fetch data'});
  });