使用Angular rxjs列印滑鼠點選事件的x坐标之和

源代碼：

ngOnInit(): void {
    const button = document.querySelector('button');
    fromEvent(button, 'click').pipe(map(event => (event as MouseEvent).x ), scan((count, clientX) => count + clientX, 0))
    .subscribe(count => console.log(`total sum of mouse event.x: ${count} `));
  }
      

代碼中使用到的MouseEvent的定義很有意思，在這裡：