Angular 6的打字机计时器

Question

我正在使用Angular 6创建HTML记分板。经过一些尝试，我想出了以下解决方案：

import {EventEmitter, Output} from '@angular/core';

export class Timer{
    private delay: number = 0;
    private interval: number = 0;
    private directionUp: boolean = true;
    time: number = 0;
    private lastTick: number;
    private intHold: number;
    private toHold: number;
    private expectedTick: number;    
    @Output() timeUp = new EventEmitter();

    constructor(_interval: number, countDown: boolean,_startTime: number ){     
        this.interval = _interval;
        if (_startTime)
            this.time = _startTime;
        if(countDown){
            this.directionUp = false;
        }
    }    
    private timeRunner(){
            this.lastTick = Date.now(); //is it ok to use Date.now()?
            if (this.directionUp) {
                this.time++;
            } else { 
                if (this.time > 0){
                    this.time--;
                } else {
                    window.clearInterval(this.intHold);
                    this.intHold=null;
                    this.timeUp.emit();
                }
            }
        }    
    run(){
        if (!this.toHold && !this.intHold) {
            var self = this;
            if (this.delay > 0) { //on stop and start I use the difference from the "expected" delay 
                this.expectedTick= Date.now() + this.delay;
                this.toHold=window.setTimeout(function(){
                    self.timeRunner();
                    self.intHold=window.setInterval(function(){self.timeRunner();}, self.interval);
                    }, this.delay);
            } else {
                self.timeRunner();
                self.intHold=window.setInterval(function(){self.timeRunner();}, self.interval);
            }
        }
    }   
    stop (stopTime: number) {
        //stopTime is needed because it may run over WebSocket
        window.clearInterval(this.intHold);
        window.clearTimeout(this.toHold);
        this.intHold = null;
        this.toHold = null;
        if (!this.expectedTick || stopTime > this.expectedTick) {
            this.delay=this.interval-(stopTime-this.lastTick);
        } else {
            //time didn't tick, so I calculate new delay
            this.delay = this.expectedTick-stopTime;
        }
    }    
    reset (_startTime: number) {
        this.time = _startTime;
    }
}

我对Date.now()的使用以及对重新启动时重新计算延迟的方式有疑问。 expectedTick的计算是否正确，或者从长远来看效率低下？计时器将是我项目的核心要素，因此我需要它非常可靠。