创建一个Observable，该Observable发出来自给定事件目标的特定类型的事件。
参数
| 参数名 | 类型 | 描述 |
|---|
target | any | The DOM EventTarget, Node.js EventEmitter, JQuery-like event target, NodeList or HTMLCollection |
eventName | string | The event name of interest, being emitted by the target. |
options | EventListenerOptions ((...args: any[]) => T) | 可选。默认值未定义。传递给底层addListener、addEventListener或on函数的选项。 |
resultSelector | (...args: any[]) => T | Optional. Default is undefined.A mapping function used to transform events. It takes the arguments from the event handler and should return a single value. |
返回
Observable<T>: 通过target的侦听器处理程序注册的Observable的发射事件。
examples
在 DOM 上发出click
import { fromEvent } from 'rxjs';
const clicks = fromEvent(document, 'click');
clicks.subscribe(x => console.log(x));
