fromEvent.ts

import { Observable } from '../Observable';
import { isArray } from '../util/isArray';
import { isFunction } from '../util/isFunction';
import { Subscriber } from '../Subscriber';
import { map } from '../operators/map';

const toString: Function = Object.prototype.toString;

export interface NodeStyleEventEmitter {
  addListener: (eventName: string | symbol, handler: NodeEventHandler) => this;
  removeListener: (eventName: string | symbol, handler: NodeEventHandler) => this;
}

export type NodeEventHandler = (...args: any[]) => void;

// For APIs that implement `addListener` and `removeListener` methods that may
// not use the same arguments or return EventEmitter values
// such as React Native
export interface NodeCompatibleEventEmitter {
  addListener: (eventName: string, handler: NodeEventHandler) => void | {};
  removeListener: (eventName: string, handler: NodeEventHandler) => void | {};
}

export interface JQueryStyleEventEmitter {
  on: (eventName: string, handler: Function) => void;
  off: (eventName: string, handler: Function) => void;
}

export interface HasEventTargetAddRemove<E> {
  addEventListener(type: string, listener: ((evt: E) => void) | null, options?: boolean | AddEventListenerOptions): void;
  removeEventListener(type: string, listener?: ((evt: E) => void) | null, options?: EventListenerOptions | boolean): void;
}

export type EventTargetLike<T> = HasEventTargetAddRemove<T> | NodeStyleEventEmitter | NodeCompatibleEventEmitter | JQueryStyleEventEmitter;

export type FromEventTarget<T> = EventTargetLike<T> | ArrayLike<EventTargetLike<T>>;

export interface EventListenerOptions {
  capture?: boolean;
  passive?: boolean;
  once?: boolean;
}

export interface AddEventListenerOptions extends EventListenerOptions {
  once?: boolean;
  passive?: boolean;
}

/* tslint:disable:max-line-length */
export function fromEvent<T>(target: FromEventTarget<T>, eventName: string): Observable<T>;
/** @deprecated resultSelector no longer supported, pipe to map instead */
export function fromEvent<T>(target: FromEventTarget<T>, eventName: string, resultSelector: (...args: any[]) => T): Observable<T>;
export function fromEvent<T>(target: FromEventTarget<T>, eventName: string, options: EventListenerOptions): Observable<T>;
/** @deprecated resultSelector no longer supported, pipe to map instead */
export function fromEvent<T>(target: FromEventTarget<T>, eventName: string, options: EventListenerOptions, resultSelector: (...args: any[]) => T): Observable<T>;
/* tslint:enable:max-line-length */

/**
 * Creates an Observable that emits events of a specific type coming from the
 * given event target.
 *
 * <span class="informal">Creates an Observable from DOM events, or Node.js
 * EventEmitter events or others.</span>
 *
 * ![](fromEvent.png)
 *
 * `fromEvent` accepts as a first argument event target, which is an object with methods
 * for registering event handler functions. As a second argument it takes string that indicates
 * type of event we want to listen for. `fromEvent` supports selected types of event targets,
 * which are described in detail below. If your event target does not match any of the ones listed,
 * you should use {@link fromEventPattern}, which can be used on arbitrary APIs.
 * When it comes to APIs supported by `fromEvent`, their methods for adding and removing event
 * handler functions have different names, but they all accept a string describing event type
 * and function itself, which will be called whenever said event happens.
 *
 * Every time resulting Observable is subscribed, event handler function will be registered
 * to event target on given event type. When that event fires, value
 * passed as a first argument to registered function will be emitted by output Observable.
 * When Observable is unsubscribed, function will be unregistered from event target.
 *
 * Note that if event target calls registered function with more than one argument, second
 * and following arguments will not appear in resulting stream. In order to get access to them,
 * you can pass to `fromEvent` optional project function, which will be called with all arguments
 * passed to event handler. Output Observable will then emit value returned by project function,
 * instead of the usual value.
 *
 * Remember that event targets listed below are checked via duck typing. It means that
 * no matter what kind of object you have and no matter what environment you work in,
 * you can safely use `fromEvent` on that object if it exposes described methods (provided
 * of course they behave as was described above). So for example if Node.js library exposes
 * event target which has the same method names as DOM EventTarget, `fromEvent` is still
 * a good choice.
 *
 * If the API you use is more callback then event handler oriented (subscribed
 * callback function fires only once and thus there is no need to manually
 * unregister it), you should use {@link bindCallback} or {@link bindNodeCallback}
 * instead.
 *
 * `fromEvent` supports following types of event targets:
 *
 * **DOM EventTarget**
 *
 * This is an object with `addEventListener` and `removeEventListener` methods.
 *
 * In the browser, `addEventListener` accepts - apart from event type string and event
 * handler function arguments - optional third parameter, which is either an object or boolean,
 * both used for additional configuration how and when passed function will be called. When
 * `fromEvent` is used with event target of that type, you can provide this values
 * as third parameter as well.
 *
 * **Node.js EventEmitter**
 *
 * An object with `addListener` and `removeListener` methods.
 *
 * **JQuery-style event target**
 *
 * An object with `on` and `off` methods
 *
 * **DOM NodeList**
 *
 * List of DOM Nodes, returned for example by `document.querySelectorAll` or `Node.childNodes`.
 *
 * Although this collection is not event target in itself, `fromEvent` will iterate over all Nodes
 * it contains and install event handler function in every of them. When returned Observable
 * is unsubscribed, function will be removed from all Nodes.
 *
 * **DOM HtmlCollection**
 *
 * Just as in case of NodeList it is a collection of DOM nodes. Here as well event handler function is
 * installed and removed in each of elements.
 *
 *
 * ## Examples
 * ### Emits clicks happening on the DOM document
 * ```ts
 * import { fromEvent } from 'rxjs';
 *
 * const clicks = fromEvent(document, 'click');
 * clicks.subscribe(x => console.log(x));
 *
 * // Results in:
 * // MouseEvent object logged to console every time a click
 * // occurs on the document.
 * ```
 *
 * ### Use addEventListener with capture option
 * ```ts
 * import { fromEvent } from 'rxjs';
 *
 * const clicksInDocument = fromEvent(document, 'click', true); // note optional configuration parameter
 *                                                              // which will be passed to addEventListener
 * const clicksInDiv = fromEvent(someDivInDocument, 'click');
 *
 * clicksInDocument.subscribe(() => console.log('document'));
 * clicksInDiv.subscribe(() => console.log('div'));
 *
 * // By default events bubble UP in DOM tree, so normally
 * // when we would click on div in document
 * // "div" would be logged first and then "document".
 * // Since we specified optional `capture` option, document
 * // will catch event when it goes DOWN DOM tree, so console
 * // will log "document" and then "div".
 * ```
 *
 * @see {@link bindCallback}
 * @see {@link bindNodeCallback}
 * @see {@link fromEventPattern}
 *
 * @param {FromEventTarget<T>} target The DOM EventTarget, Node.js
 * EventEmitter, JQuery-like event target, NodeList or HTMLCollection to attach the event handler to.
 * @param {string} eventName The event name of interest, being emitted by the
 * `target`.
 * @param {EventListenerOptions} [options] Options to pass through to addEventListener
 * @return {Observable<T>}
 * @name fromEvent
 */
export function fromEvent<T>(
  target: FromEventTarget<T>,
  eventName: string,
  options?: EventListenerOptions | ((...args: any[]) => T),
  resultSelector?: ((...args: any[]) => T)
): Observable<T> {

  if (isFunction(options)) {
    // DEPRECATED PATH
    resultSelector = options;
    options = undefined;
  }
  if (resultSelector) {
    // DEPRECATED PATH
    return fromEvent<T>(target, eventName, <EventListenerOptions | undefined>options).pipe(
      map(args => isArray(args) ? resultSelector(...args) : resultSelector(args))
    );
  }

  return new Observable<T>(subscriber => {
    function handler(e: T) {
      if (arguments.length > 1) {
        subscriber.next(Array.prototype.slice.call(arguments));
      } else {
        subscriber.next(e);
      }
    }
    setupSubscription(target, eventName, handler, subscriber, options as EventListenerOptions);
  });
}

function setupSubscription<T>(sourceObj: FromEventTarget<T>, eventName: string,
                              handler: (...args: any[]) => void, subscriber: Subscriber<T>,
                              options?: EventListenerOptions) {
  let unsubscribe: () => void;
  if (isEventTarget(sourceObj)) {
    const source = sourceObj;
    sourceObj.addEventListener(eventName, handler, options);
    unsubscribe = () => source.removeEventListener(eventName, handler, options);
  } else if (isJQueryStyleEventEmitter(sourceObj)) {
    const source = sourceObj;
    sourceObj.on(eventName, handler);
    unsubscribe = () => source.off(eventName, handler);
  } else if (isNodeStyleEventEmitter(sourceObj)) {
    const source = sourceObj;
    sourceObj.addListener(eventName, handler as NodeEventHandler);
    unsubscribe = () => source.removeListener(eventName, handler as NodeEventHandler);
  } else if (sourceObj && (sourceObj as any).length) {
    for (let i = 0, len = (sourceObj as any).length; i < len; i++) {
      setupSubscription(sourceObj[i], eventName, handler, subscriber, options);
    }
  } else {
    throw new TypeError('Invalid event target');
  }

  subscriber.add(unsubscribe);
}

function isNodeStyleEventEmitter(sourceObj: any): sourceObj is NodeStyleEventEmitter {
  return sourceObj && typeof sourceObj.addListener === 'function' && typeof sourceObj.removeListener === 'function';
}

function isJQueryStyleEventEmitter(sourceObj: any): sourceObj is JQueryStyleEventEmitter {
  return sourceObj && typeof sourceObj.on === 'function' && typeof sourceObj.off === 'function';
}

function isEventTarget(sourceObj: any): sourceObj is HasEventTargetAddRemove<any> {
  return sourceObj && typeof sourceObj.addEventListener === 'function' && typeof sourceObj.removeEventListener === 'function';
}