点击aa,数字加一，点击bb,数字减一,数字最小值不能为0,不能为负数.

<a href="#">-</a><input value="1" type="text" /><a href="#">+</a>

解决方案 »

  1.   

    <html>
    <head>
        <title>Log Out</title>
        <meta http-equiv='Pragma' content='no-cache'>
        <script type="text/javascript">
            onload = function () {
                var numId = document.getElementById("num");
                var numIn = numId.value;            function isPositive(num) {
                    if (num > 0)
                        return true;
                    else
                        return false;
                }
                document.getElementById("sub").onclick = function () {
                    if (isPositive(numId.value-1))
                        numId.value--;
                    else
                        alert("数字错误");
                }
                document.getElementById("add").onclick = function () {
                    if (isPositive(numId.value))
                        numId.value++;
                    else
                        alert("数字错误");
                }
            }
        </script>
    </head>
    <body>
    <a href="#" id="sub">-</a><input value="1" type="text" id="num"/><a href="#" id="add">+</a>
    </body>
    </html>
      

  2.   

    <a href="javascript:void(0)" onclick="sum(-1)">-</a>
    <input value="1" type="text" readonly="readonly" id="num"/>
    <a href="javascript:void(0)" onclick="sum(1)">+</a>
    <script>
    var i=1;
    function sum(n){
      i+=n;
      if(i<1)i=1;
      document.getElementById("num").value=i;
    }
    </script>