加減乘除`add` `sub` `mul` `div`
計算之前判斷數字是否存在 避免報錯或出現NaN
```
// 數據改變
handleChange(value, key, column, record) {
this.record = record;
const newData = [...this.dataSource];
let target = newData.filter((item) => key === item.id)[0];
if (target) {
target[column] = value;
newData.forEach((ele) => {
if (!!ele.excludingTax && !!ele.amountTax) {
ele.amountTotal = this.add(ele.excludingTax, ele.amountTax);
} else {
ele.amountTotal = this.add(ele.excludingTax, ele.amountTax);
}
});
this.dataSource = newData;
}
},
```
