es6/observable/FromEventPatternObservable.js

import { isFunction } from '../util/isFunction';
import { Observable } from '../Observable';
import { Subscription } from '../Subscription';
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @extends {Ignored}
 * @hide true
 */
export class FromEventPatternObservable extends Observable {
    constructor(addHandler, removeHandler, selector) {
        super();
        this.addHandler = addHandler;
        this.removeHandler = removeHandler;
        this.selector = selector;
    }
    /**
     * 从一个基于 addHandler/removeHandler 方法的API创建 Observable。
     *
     * <span class="informal">将任何 addHandler/removeHandler 的API转化为 Observable。</span>
     *
     * <img src="./img/fromEventPattern.png" width="100%">
     *
     * 创建 Observable ，该 Observable 通过使用`addHandler` 和 `removeHandler`添加和删除事件处理器,
     * 使用可选的选择器函数将事件参数转化为结果. `addHandler`当输出 Observable 被订阅的时候调用, `removeHandler`
     * 方法在取消订阅的时候被调用。
     *
     * @example <caption>发出 DOM document 上的点击事件</caption>
     * function addClickHandler(handler) {
     *   document.addEventListener('click', handler);
     * }
     *
     * function removeClickHandler(handler) {
     *   document.removeEventListener('click', handler);
     * }
     *
     * var clicks = Rx.Observable.fromEventPattern(
     *   addClickHandler,
     *   removeClickHandler
     * );
     * clicks.subscribe(x => console.log(x));
     *
     * @see {@link from}
     * @see {@link fromEvent}
     *
     * @param {function(handler: Function): any} addHandler 一个接收处理器的函数，并且将
     * 该处理器添加到事件源。
     * @param {function(handler: Function, signal?: any): void} [removeHandler] 可选的
     * 函数，接受处理器函数做为参数，可以移除处理器当之前使用`addHandler`添加处理器。如果 addHandler
     * 返回的信号当移除的时候要清理，removeHandler 会去做这件事情。
     * @param {function(...args: any): T} [selector] 可选的函数处理结果。 接受事件处理的参数返
     * 回单个的值。
     * @return {Observable<T>}
     * @static true
     * @name fromEventPattern
     * @owner Observable
     */
    static create(addHandler, removeHandler, selector) {
        return new FromEventPatternObservable(addHandler, removeHandler, selector);
    }
    _subscribe(subscriber) {
        const removeHandler = this.removeHandler;
        const handler = !!this.selector ? (...args) => {
            this._callSelector(subscriber, args);
        } : function (e) { subscriber.next(e); };
        const retValue = this._callAddHandler(handler, subscriber);
        if (!isFunction(removeHandler)) {
            return;
        }
        subscriber.add(new Subscription(() => {
            //TODO: determine whether or not to forward to error handler
            removeHandler(handler, retValue);
        }));
    }
    _callSelector(subscriber, args) {
        try {
            const result = this.selector(...args);
            subscriber.next(result);
        }
        catch (e) {
            subscriber.error(e);
        }
    }
    _callAddHandler(handler, errorSubscriber) {
        try {
            return this.addHandler(handler) || null;
        }
        catch (e) {
            errorSubscriber.error(e);
        }
    }
}
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