<input type="text" class="input" id="code_num" maxlength="4" style="position: relative; float: left;width: 100px;height: 30px" />
$("#code_num").change(function(){});
<input type="text" class="input" id="code_num" maxlength="4" style="position: relative; float: left;width: 100px;height: 30px" />
$("#code_num").change(function(){});