topic description

when using koa-router to process url routing in nodeJS"s KOA framework, the front end cannot get the server return value

sources of topics and their own ideas

related codes

/ / Please paste the code text below (do not replace the code with pictures)
front-end JavaScript:

$.ajax({
    type: "POST",
    url: "http://127.0.0.1:8081/uploadimgs",
    data:formData, 
    dataType: "json", //json
    //FormData
    cache:false,  //true
    processData:false, //datafalse;trueFormDataString
    contentType:false,  //httpfalse
    success: function(msg){
    console.log("msg: "+msg);
    console.log("");

        //ajaxbase64
        //
        var outputDir="C:/ajax/output/"+$port.toLowerCase();
        console.log("outputDir: "+outputDir);

        //
        $.ajax({
            type: "POST",
            url:"http://127.0.0.1:8081/backImgs",
            data:{
                outdir:outputDir
            },
            dataType:"json",
            //
            success:function(msg){
                console.log("msg: "+msg);
                subAndJump(msg);                      
            },
            error:function(err){
                console.log("...");
                console.log(err);
            }
        });

            },
    error:function(){
        console.log("ajax");
    }
    });                  

backend nodeJS app.js

router.post("/uploadimgs",async (ctx,next) => {
    //
    childProcessExit=false;

    let form = new multiparty.Form({
        uploadDir:"C:/ajax/input/",
        keepExtensions:true,//
        autoFields:true,
        autoFiles:true
        });

    //JSON
    let errsign={status:500,exception:null};
    let datasign={status:200,recordset:null};
    //loadimg()
     function loadimg() {
        let send_json={};
        return  new Promise((resolve,reject)=>{
            form.parse(ctx.req,function(err,fields,files){
                if(err){
                    // throw err;
                    console.log(err);//Error: write after end
                    send_json={
                        exception:"",
                        err:false
                    };
                    resolve(send_json);
                    // return send_json;
                }else{
                    //
                    controlMessage.port=fields.port;
                    controlMessage.nameCH=fields.name_ch;
                    controlMessage.nameEN=fields.name_en;
                    send_json={
                        recordset:"",
                        err:true}
                    resolve(send_json);
                    let workProcess=exec("python C:/ajax/main.py " +controlMessage.nameCH+" "+controlMessage.nameEN+" "+controlMessage.port+" ",function(error,stdout,stderr){
                        if(stdout.length >1){
                            console.log("you offer args:"+stdout);
                        } else {
                            console.log("you don\"t offer args");
                        }
                        if(error) {
                            console.info("stderr : "+stderr);
                        }
                    });

                    workProcess.on("exit",(code)=>{
                        console.log(":"+code);
                        childProcessExit=true;//true

                        console.log("childProcessExit: "+childProcessExit);
                    });
                }
            });

            //
            form.on("file",(name,file)=>{
                // console.log("fileName="+file.fieldName);
                // console.log("originalFilename="+file.originalFilename);
                // console.log("path="+file.path);
                fs.rename(file.path,"C:/ajax/input/"+file.originalFilename,(err)=>{
                    if(err){
                        throw err;
                    }
                })
            
            });

        });
    }
    await loadimg().then(sendjson=>{
        // console.log("sendjson = "+sendjson);
        if(sendjson.err===false){
            errsign["exception"]=sendjson.exception;
            ctx.body=errsign;
        }else{
            datasign["recordset"]=sendjson.recordset;
            ctx.body=datasign;
        }
    });
});

//post
router.post("/backImgs",async (ctx,next)=>{
    
    console.log("");
    var num=0;
    //
    var timer=setInterval(async function(){
        numPP;
        console.log(""+num+"");
        if(childProcessExit){
            console.log(1);
            clearInterval(timer);
            await pictureTrans().then(picBase64=>{
                ctx.body=picBase64;
            });
        }

        //6s
        if(num>6){
            clearInterval(timer);
            throw new Error(",...");
        }
    },1000);


    function pictureTrans(){
        return new Promise((resolve,reject)=>{
            console.log("pictureTrans")
            let  dir=ctx.request.body.outdir;
            console.log(`: ${dir}...`);
            //
            var filePath = path.resolve(dir);
        
            //
            fs.readdir(filePath,function(err,files){
                if(err){
                    console.warn(err)
                }else{
        
                    //base64
                    var picBase64={};
                    //
                    files.forEach(function(filename){
                        //
                        var filedir = path.join(filePath,filename);
                        //fs.Stats
                        fs.stat(filedir,function(eror,stats){
                            if(eror){
                                console.warn("stats");
                            }else{
                                var isFile = stats.isFile();//
                                var isDir = stats.isDirectory();//
                                if(isFile){
                                    console.log(`: ${filedir}...`);
                                    let data = fs.readFileSync(filedir);
                                
                                    data = new Buffer(data).toString("base64");
                                    console.log("data: "+data);
                                    console.log(`data: ${typeof data}`);
                                    console.log("filename: "+filename);
                                    picBase64[filename]=data;
                                    console.log(`picBase64.${filename}: ${picBase64[filename]}`);
                                }
                                if(isDir){
                                    fileDisplay(filedir);//
                                }
                            }
                        })
                    });
                    //base64
                    console.log("base64");
                    resolve(picBase64);
                }
            });

        });
    }

    //console.log("dir:"+ctx.request.body.outdir);
    //,childProcessExit
    //true,base64
});

app.use(router.routes());
app.listen(8081);

what result do you expect? What is the error message actually seen?

I see that the / uploadimgs access from the front end to the background was successful, and the message msg, and access / backImags failed.
the following is the console print:
console:

network:

PS:app.js shows that the file is read normally and has been successfully converted to base64 bit encoding

online, etc., ask the boss to provide some solutions OTZ