JS 实现停止和继续倒计时

即使自己很菜，也要一点一点的爬，总有一天可以成为大佬级的人物，

 
<button class="btn1">发送验证码</button>

<button class="btn2">停止</button>

<button class="btn3">继续</button>

<script type="text/javascript" src="1.js"></script>

1.js

function countNum(cb1,cb2,num){

    let count;
    let timer = null;
    if(num){
        count = num;
    }else{
        count = 60
    }
    timer = setInterval((num)=>{
        if(count != 0){
            count--;
            cb1(count)

        }else{
            clearInterval(timer)
            cb2 && cb2()
            return false;
        }
    },1000)
    return timer
}

let btn = document.querySelector('.btn1')
let btn2 = document.querySelector('.btn2')
let btn3 = document.querySelector('.btn3')
btn.addEventListener('click',()=>{
    console.log(this)
    this.a = this.countNum((time)=>{
            btn.innerText = time;
            return time;
        },()=>{
            btn.innerText = '发送验证码';

        },null)
},false)

btn2.addEventListener('click',()=>{
    console.log(this)
    clearInterval(this.a)
},false)

btn3.addEventListener('click',()=>{
    console.log(btn)
    this.a = this.countNum((time)=>{
        btn.innerText = time;
    },()=>{
        btn.innerText = '发送验证码';
    },btn.innerText)

},false)

菜鸟只能想到这种方法，如果有更好的方法，衷心希望不吝赐教。万分感谢