求利润 利润等于售价减进价 输入进价和售价后，自动利润算出并填到文本框中，

<div class="modal-dialog">
    <div class="modal-content">
        <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal"
                aria-hidden="true">
                &times;
            </button>
            <h4 class="modal-title" id="myModalLabel">
                <%=isAdd?"添加":"修改" %>商品名称:
            </h4>
        </div>
        <div class="jarviswidget" id="wid-id-0" data-widget-colorbutton="false" data-widget-editbutton="false" data-widget-deletebutton="false" data-widget-sortable="false">
            <div>
                <div class="widget-body">
                    <form id="userForm" class="" 
                        action="<%=path %>/intercity/addIntercity.do" method="post">
                        <input type="hidden" name="goodsId" value="<%=Global.nvlToString(goods.getGId())%>">
                        <fieldset>
                            <div class="form-group">
                                <div class="row">
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">商品ID</label>
                                        <input type="text" class="form-control"  maxlength="32" name="gId" value="<%=Global.nvlToString(goods.getGId())%>">
                                    </div>
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">商品名称</label>
                                        <input type="text" class="form-control" maxlength="16" name="gName" value="<%=Global.nvlToString(goods.getGName())%>">
                                    </div>
                                </div>
                            </div>      
                        </fieldset>
                        <fieldset>
                            <div class="form-group">
                                <div class="row">
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">进货价格</label>
                                        <input type="text" class="form-control" maxlength="32" name="gPurchaseprice"  value="<%=Global.nvlToString(goods.getGPurchaseprice())%>">
                                    </div>
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">销售价格</label>
                                        <input type="text" class="form-control" maxlength="20" name="gSellprice"  value="<%=Global.nvlToString(goods.getGSellprice())%>">
                                    </div>
                                </div>  
                            </div>
                        </fieldset>
                        <fieldset>
                            <div class="form-group">
                                <div class="row">
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">库存量</label>
                                        <input type="text" class="form-control" maxlength="16" name="gAmount" value="<%=Global.nvlToString(goods.getGAmount())%>">
                                    </div>
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">供应商</label>
                                        <input type="text" class="form-control" maxlength="32" name="sId" value="<%=Global.nvlToString(goods.getSId())%>">
                                    </div>
                                </div>
                            </div>      
                        </fieldset>
                        <fieldset>
                            <div class="form-group">
                                <div class="row">
                                    <div class="col-sm-12 col-md-4">
                                        <label class="control-label">备注</label>
                                        <input type="text" class="form-control" maxlength="32" name="gMemo" value="<%=Global.nvlToString(goods.getGMemo())%>">
                                    </div>
                                    <div class="col-sm-12 col-md-4" >
                                        <label class="control-label">利润</label>
                                        <input type="submit" class="form-control" maxlength="16" name="gProfit" value="<%=Global.nvlToString(goods.getGProfit())%>">
                                    </div>
                                </div>
                            </div>      
                        </fieldset>
                        <div class="form-actions">
                                <div class="row">
                                    <div class="col-md-12">
                                        <button class="btn btn-default" type="submit" id="add">
                                            <i class="fa fa-eye"></i>
                                            提交
                                        </button>
                                    </div>
                                </div>
                        </div>
                    </form>
                </div>

            </div>
            <!-- end widget content -->

        </div>

    </div>
    <!-- /.modal-content -->
</div>
<!-- /.modal-dialog -->

写一个js函数，获取文本框中的数据，然后计算；
得到的结果可以直接用innerText显示在文本框中，
该动的手绝不能偷懒呀~~

写一个js函数，当用户输入进价或者售价触发函数，如果进价或者售价有一个没有输入值那么就不计算利润，如果都有值则计算利润并$("#id").val()赋值到文本框