净额未以正确的方式工作。javascript 计算出错 [重复]

问：

我正在尝试制作发票脚本。使用 js 执行的计算部分。手动输入总金额和增值税百分比。增值税金额显示正常。但净额添加并不完美。代码如下。

JS系列

$(document).on("change keyup blur", "#caVat", function() {
        var gross = $('#caGross').val();
        var vat = $('#caVat').val();            
        var dec = (vat / 100).toFixed(2); //its convert 10 into 0.10
        var mult = gross * dec; // gives the value for subtract from main value
        var discont = gross - mult; 
        var add = gross + mult;
        $('#caVatamnt').val(mult);
        $('#caNetamnt').val(add);
    });

HTML 代码

                   <div class="form-row" style="padding-top: 10px;">
                                    <div class="col">
                                        <h5>Notes:</h5><textarea class="form-control" rows="8"></textarea>
                                    </div>
                                    <div class="col">
                                        <div class="box-bg">
                                            <div class="form-row text-dark">
                                                <div class="col-xl-5 offset-xl-0 align-self-center">
                                                    <h6 class="mb-0 font-sm">Gross amount:</h6>
                                                </div>
                                                <div class="col-xl-7 offset-xl-0 text-right align-self-center">
                                                    <div class="form-group mb-1"><input class="form-control form-control-sm font-sm" type="number" name="pogrossamount" id="caGross"></div>
                                                </div>
                                                <div class="col-xl-5 offset-xl-0 align-self-center">
                                                    <h6 class="mb-0 font-sm">VAT (%):</h6>
                                                </div>
                                                <div class="col-xl-7 offset-xl-0 text-right align-self-center">
                                                    <div class="form-group mb-1"><input class="form-control form-control-sm font-sm" type="text" name="povat" id="caVat" ></div>
                                                </div>
                                                <div class="col-xl-5 offset-xl-0 align-self-center">
                                                    <h6 class="mb-0 font-sm">TAX Amount:</h6>
                                                </div>
                                                <div class="col-xl-7 offset-xl-0 text-right align-self-center">
                                                    <div class="form-group mb-1"><input class="form-control form-control-sm font-sm" type="text" name="potax" id="caVatamnt" readonly ></div>
                                                </div>
                                                <div class="col-xl-5 offset-xl-0 align-self-center">
                                                    <h6 class="mb-0 font-sm">Discount:</h6>
                                                </div>
                                                <div class="col-xl-7 offset-xl-0 text-right align-self-center">
                                                    <div class="form-group mb-1"><input class="form-control form-control-sm font-sm" type="number" name="podiscount" ></div>
                                                </div>
                                                <div class="col-xl-5 offset-xl-0 align-self-center">
                                                    <h6 class="mb-0 font-sm">Net amount:</h6>
                                                </div>
                                                <div class="col-xl-7 offset-xl-0 text-right align-self-center">
                                                    <div class="form-group mb-1"><input class="form-control form-control-sm font-sm" type="number" name="ponetamount" id="caNetamnt" readonly ></div> 
                                                     </div>
                                                <div class="col text-right"> <input class= "genric-btn success circle arrow" type="submit" name="submit" value="submit"><a class="genric-btn warning circle arrow" role="button" style="padding-top: 6px;margin-top: 5px;margin-left: 10px;color: rgb(255,255,255);background: #032c71;" href="window.print();">Print</a></div>
                                            </div>
                                        </div>
                                    </div>
                                </div>
                            </div>
                        </form>

结果在这里输入图像描述，我得到：