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import { Observable } from '../Observable';
import { isArray } from '../util/isArray';
import { isFunction } from '../util/isFunction';
import { NodeEventHandler } from './fromEvent';
import { map } from '../operators/map';
/* tslint:disable:max-line-length */
export function fromEventPattern<T>(addHandler: (handler: NodeEventHandler) => any, removeHandler?: (handler: NodeEventHandler, signal?: any) => void): Observable<T>;
/** @deprecated resultSelector no longer supported, pipe to map instead */
export function fromEventPattern<T>(addHandler: (handler: NodeEventHandler) => any, removeHandler?: (handler: NodeEventHandler, signal?: any) => void, resultSelector?: (...args: any[]) => T): Observable<T>;
/* tslint:enable:max-line-length */
/**
* Creates an Observable from an arbitrary API for registering event handlers.
*
* <span class="informal">When that method for adding event handler was something {@link fromEvent}
* was not prepared for.</span>
*
* 
*
* `fromEventPattern` allows you to convert into an Observable any API that supports registering handler functions
* for events. It is similar to {@link fromEvent}, but far
* more flexible. In fact, all use cases of {@link fromEvent} could be easily handled by
* `fromEventPattern` (although in slightly more verbose way).
*
* This operator accepts as a first argument an `addHandler` function, which will be injected with
* handler parameter. That handler is actually an event handler function that you now can pass
* to API expecting it. `addHandler` will be called whenever Observable
* returned by the operator is subscribed, so registering handler in API will not
* necessarily happen when `fromEventPattern` is called.
*
* After registration, every time an event that we listen to happens,
* Observable returned by `fromEventPattern` will emit value that event handler
* function was called with. Note that if event handler was called with more
* then one argument, second and following arguments will not appear in the Observable.
*
* If API you are using allows to unregister event handlers as well, you can pass to `fromEventPattern`
* another function - `removeHandler` - as a second parameter. It will be injected
* with the same handler function as before, which now you can use to unregister
* it from the API. `removeHandler` will be called when consumer of resulting Observable
* unsubscribes from it.
*
* In some APIs unregistering is actually handled differently. Method registering an event handler
* returns some kind of token, which is later used to identify which function should
* be unregistered or it itself has method that unregisters event handler.
* If that is the case with your API, make sure token returned
* by registering method is returned by `addHandler`. Then it will be passed
* as a second argument to `removeHandler`, where you will be able to use it.
*
* If you need access to all event handler parameters (not only the first one),
* or you need to transform them in any way, you can call `fromEventPattern` with optional
* third parameter - project function which will accept all arguments passed to
* event handler when it is called. Whatever is returned from project function will appear on
* resulting stream instead of usual event handlers first argument. This means
* that default project can be thought of as function that takes its first parameter
* and ignores the rest.
*
* ## Example
* ### Emits clicks happening on the DOM document
*
* ```ts
* import { fromEventPattern } from 'rxjs';
*
* function addClickHandler(handler) {
* document.addEventListener('click', handler);
* }
*
* function removeClickHandler(handler) {
* document.removeEventListener('click', handler);
* }
*
* const clicks = fromEventPattern(
* addClickHandler,
* removeClickHandler
* );
* clicks.subscribe(x => console.log(x));
*
* // Whenever you click anywhere in the browser, DOM MouseEvent
* // object will be logged.
* ```
*
* ## Example
* ### Use with API that returns cancellation token
*
* ```ts
* import { fromEventPattern } from 'rxjs';
*
* const token = someAPI.registerEventHandler(function() {});
* someAPI.unregisterEventHandler(token); // this APIs cancellation method accepts
* // not handler itself, but special token.
*
* const someAPIObservable = fromEventPattern(
* function(handler) { return someAPI.registerEventHandler(handler); }, // Note that we return the token here...
* function(handler, token) { someAPI.unregisterEventHandler(token); } // ...to then use it here.
* );
* ```
*
* ## Example
* ### Use with project function
*
* ```ts
* import { fromEventPattern } from 'rxjs';
*
* someAPI.registerEventHandler((eventType, eventMessage) => {
* console.log(eventType, eventMessage); // Logs "EVENT_TYPE" "EVENT_MESSAGE" to console.
* });
*
* const someAPIObservable = fromEventPattern(
* handler => someAPI.registerEventHandler(handler),
* handler => someAPI.unregisterEventHandler(handler)
* (eventType, eventMessage) => eventType + " --- " + eventMessage // without that function only "EVENT_TYPE"
* ); // would be emitted by the Observable
*
* someAPIObservable.subscribe(value => console.log(value));
*
* // Logs:
* // "EVENT_TYPE --- EVENT_MESSAGE"
* ```
*
* @see {@link fromEvent}
* @see {@link bindCallback}
* @see {@link bindNodeCallback}
*
* @param {function(handler: Function): any} addHandler A function that takes
* a `handler` function as argument and attaches it somehow to the actual
* source of events.
* @param {function(handler: Function, token?: any): void} [removeHandler] A function that
* takes a `handler` function as an argument and removes it from the event source. If `addHandler`
* returns some kind of token, `removeHandler` function will have it as a second parameter.
* @param {function(...args: any): T} [project] A function to
* transform results. It takes the arguments from the event handler and
* should return a single value.
* @return {Observable<T>} Observable which, when an event happens, emits first parameter
* passed to registered event handler. Alternatively it emits whatever project function returns
* at that moment.
* @static true
* @name fromEventPattern
* @owner Observable
*/
export function fromEventPattern<T>(addHandler: (handler: NodeEventHandler) => any,
removeHandler?: (handler: NodeEventHandler, signal?: any) => void,
resultSelector?: (...args: any[]) => T): Observable<T | T[]> {
if (resultSelector) {
// DEPRECATED PATH
return fromEventPattern<T>(addHandler, removeHandler).pipe(
map(args => isArray(args) ? resultSelector(...args) : resultSelector(args))
);
}
return new Observable<T | T[]>(subscriber => {
const handler = (...e: T[]) => subscriber.next(e.length === 1 ? e[0] : e);
let retValue: any;
try {
retValue = addHandler(handler);
} catch (err) {
subscriber.error(err);
return undefined;
}
if (!isFunction(removeHandler)) {
return undefined;
}
return () => removeHandler(handler, retValue) ;
});
}