<dl class="row">

      <dt class="tit">

          <label for="title"><em>*</em>编号</label>

      </dt>

      <dd class="opt">

         <input type="text" name="number" value="" id="number" class="input-txt" maxlength="100">

         <span class="err"></span>

         <p class="notic"></p>

      </dd>

</dl>

    function randomStr(len, arr) {

        var ans = '';

        for(var i = len; i > 0; i--) {

            ans +=

                arr[Math.floor(Math.random() * arr.length)];

        }

        return ans;

    }

    $(function () {

        var number = randomStr(8, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789');

        $("#number").attr("value",number);//替换掉input的value值

    })