在这段代码中，为什么在发布之前执行，为什么我必须在下拉列表中选择 2 个值，然后才能将其存储在变量中？

如何解决在这段代码中，为什么在发布之前执行，为什么我必须在下拉列表中选择 2 个值，然后才能将其存储在变量中？

我的代码有两个错误，app.get 在 app.post 之前执行，我必须在将值存储在变量中之前在下拉列表中选择 2 个不同的值

nodejs：getBrandandManufacturer1 从医学数据库返回详细信息，其中品牌名称匹配并存储在数组中。 getBrandandManufacturer 将数组发送到前端

    var testvar=[];
    let getBrandandManufacturersql1 = `SELECT * FROM medicinedatabase where Brandname=? `;
    app.post("/getBrandandManufacturer1",(req,res) => {
        var jtBrandname = req.body.Brandname;
        db.query(getBrandandManufacturersql1,[jtBrandname],(err,result) => {
            if (err) {
                console.log(err);
            } else {
                testvar.push(result)
                //res.send(result)
                console.log("getBrandandManufacturersql",testvar)
            }
    
        });
    });
    
    app.get("/getBrandandManufacturer",res) => {
                res.send(testvar)
                console.log("getBrandandManufacturersql2",testvar)
             
      
    });

Reactjs ：当值选择值时，查询在onchange

中执行

    const [Brandname,setBrandname] = useState();
    const [Manufacturer,setManufacturer] = useState();
    const [brandnamemedicineList,setbrandnamemedicineList] = useState([])
    const [manufacmedicineList,setmanufacmedicineList] = useState([])
    <div className="addMed">
                <div className ="inputcss">
    
                    <select className="inputfield" name="Brand Name" onChange={(event) => {
                        setBrandname(event.target.value);;
                        console.log("brandname",Brandname)
                        Axios.post('http://localhost:3001/getBrandandManufacturer1',{
                            Brandname: Brandname,}).then(() => {
                          console.log("Success!");
                        });
                        Axios.get('http://localhost:3001/getBrandandManufacturer').then((response) => {
                            setmanufacmedicineList(response.data);
                             console.log("Update",response)
                   });
                    }}>
                        {brandnamemedicineList.map((e,key) => {
                            return <option  value={e.Brandname}>{e.Brandname}</option>;
                        })}
                    </select>
    
                    <select  className="inputfield" name="Manufacturer" onChange={(event) => {setManufacturer(event.target.value);}}>
                        {manufacmedicineList.map((e,key) => {
                            return <option  value={e.Manufacturer}>{e.Manufacturer}</option>;
                        })}
                    </select>