Lightweight Angular service detects when a user is inactive

inactive-user.service.ts

import { Injectable } from '@angular/core';

import { fromEvent, merge } from 'rxjs';
import { throttleTime } from 'rxjs/operators';

@Injectable({ providedIn: 'root' })
export class InactiveUserService {
  public inactive: boolean;
  private timer: NodeJS.Timer;

  private activity = merge(
    fromEvent(document, 'click'),
    fromEvent(document, 'scroll'),
    fromEvent(document, 'mousemove')
  );

  constructor() {
    this.activity.pipe(throttleTime(5000)).subscribe(() => {
      this.handleActivity();
    });
  }

  private handleActivity() {
    this.inactive = false;

    if (this.timer) {
      clearTimeout(this.timer);
    }

    this.waitForUserToBeInactive();
  }

  private waitForUserToBeInactive() {
    this.timer = setTimeout(() => this.inactive = true, 60000);
  }
}