js实现点赞效果

<div class="dian">
 <div id="zan">
 <img src="images/college_Likes_ic3.png" alt="很棒，赞一个">
 <div id="num1">30</div>
 </div>
  <div id="cai">
   <img src="images/college_Likes_ic.png" alt="不行，踩一下">
   <div id="num2">30</div>
 </div>
</div>

.dian {
  display: flex;
  flex-direction: row;
}

#zan,
#cai {
  width: 55px;
  height: 22px;
  display: flex;
  flex-direction: row;
  justify-content: space-between;
  background-color: #F3F3F3;
  margin: 0 10px;
  border-radius: 6px;
  user-select: none;
  cursor: pointer;
}

#zan img,
#cai img {
  width: 14px;
  height: 14px;
  margin: 5px 5px 0 5px;
}

#zan #num1,
#cai #num2 {
  line-height: 22px;
  margin-right: 3px;
}

var zan = document.getElementById('zan');
var cai = document.getElementById('cai');
var num1 = document.getElementById('num1');
var num2 = document.getElementById('num2');
var flag1 = 0;
var flag2 = 0;
zan.onclick = function() {
  if (flag1 == 0) {
    num1.innerHTML++;
  }
  if (flag1 == 1) {
    num1.innerHTML--;
  }
  if (flag1 == 2) {
    num1.innerHTML++;
    flag1 = 0;
  }
  flag1++;
}
cai.onclick = function() {
  if (flag2 == 0) {
    num2.innerHTML++;
  }
  if (flag2 == 1) {
    num2.innerHTML--;
  }
  if (flag2 == 2) {
    num2.innerHTML++;
    flag2 = 0;
  }
  flag2++;
}