求快看看 实现数量增加部分有什么问题


<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>动态改变购买数量</title>
    <link href="css/detail.css" rel="stylesheet" />
    <script>

        function numcheck()
        {
            var w=document.getElementById("buycount").value;
            var reg=/^\-[1-9][0-9]*$/;
            if(reg.test(w))
            {
                return true;
            }
            else{
                return false;
            }

        }

        //编写函数实现数量增加
        function addBuynum()
        {
            var num=document.getElementById('buycount');
            if(num)
            {
                return;
            }
            num++;
            document.getElementById().innerHTMLdocument.getElementById('buycount').innerHTML=num;
            $('#buycount').val(num);
        }
    </script>
</head>
<body>
<div class="prod-buychoose">
    <dl class="pProps" id="choosenum">
        <dt>购买数量： </dt>
        <dd id="choose-num"><a class="reduce" id="reduce1" ></a>
            <input id="buycount" value="1" onclick="numcheck()" />
            <a class="add" id="add1" onclick="addBuynum()"></a>
        </dd>
    </dl>
</div>
</body>
</html>


 
<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>动态改变购买数量</title>
    <link href="css/detail.css" rel="stylesheet" />
    <script>
 
        function numcheck()
        {
            var w=document.getElementById("buycount").value;
            var reg=/^\-[1-9][0-9]*$/;
            if(reg.test(w))
            {
                return true;
            }
            else{
                return false;
            }
 
        }
 
        //编写函数实现数量增加
        function addBuynum()
        {
            var num=document.getElementById('buycount').value;
            if(!num)
            {
                return;
            }
            num++;
          document.getElementById('buycount').value=num;
        }
    </script>
</head>
<body>
<div class="prod-buychoose">
    <dl class="pProps" id="choosenum">
        <dt>购买数量： </dt>
        <dd id="choose-num"><a class="reduce" id="reduce1" ></a>
            <input id="buycount" value="1" onclick="numcheck()" />
            <a class="add" id="add1" onclick="addBuynum()">增加</a>
        </dd>
    </dl>
</div>
</body>
</html>


function addBuynum() {
                 var input = document.getElementById('buycount');
                ++input.value
             }

script 改成这个就行了
用document.getElementById("buycount").value = ++num; 赋值

  <script>
      function numcheck() {
        var w = document.getElementById("buycount").value;
        var reg = /^\-[1-9][0-9]*$/;
        return reg.test(w);
      }

      //编写函数实现数量增加
      function addBuynum() {
        var num = document.getElementById("buycount").value;
        if (!num) {
          return;
        }
        document.getElementById("buycount").value = ++num;
      }
    </script>