input框的赋值问题

Question

html<button id="plusCount" class="plus-f" type="button" onclick="buyNumber('inputNum','add')">                        <i class="layui-icon layui-icon-add-1"></i>                    </button>                    <input id="inputNum" type="text" value="1" autocomplete="off">                    <button id="minusCount" class="minus-f" type="button" onclick="buyNumber('inputNum','del')">                        <div class="minus"></div>                    </button>js：function buyNumber(inputNum,flag){            var inputNum = document.getElementById("inputNum");            if(flag == "del") {                inputNum.value = parseInt(inputNum.value) - 1;                console.log(inputNum.value);            }else{                    inputNum.value = parseInt(inputNum.value) + 1;                    console.log(inputNum.value);            }        }后台可以看到value值的变化，但是在input框里没有变化。