13.5.14 - throttleTime

节流，可观察对象高频次向外部发出数据流，通过 throttleTime 限制在规定时间内每次只向订阅者传递一次数据流

import { fromEvent } from "rxjs"
import { throttleTime } from "rxjs/operators"
fromEvent(document, "click")
  .pipe(throttleTime(2000))
  .subscribe(x => console.log(x))