节点 js 中是否有类似 angular $watch 的东西

Question

I'm rookie in Web services and my knowledges are not so deep in node js, so I apologize in advance if the question is not correct. My Question is I have two functions in my angular-node js app. First function, uploading file to public folder on server

  var storage = multer.diskStorage({ //multers disk storage settings
    destination: function (req, file, cb) {
        cb(null, './demo/');
    },
    filename: function (req, file, cb) {
        //var datetimestamp = Date.now();
        cb(null, file.originalname
            //file.fieldname + '-' + datetimestamp + '.' + file.originalname.split('.')[file.originalname.split('.').length -1]
        );
    }
});
var upload = multer({ //multer settings
    storage: storage
}).single('file');
/** API path that will upload the files */
app.post('/upload', function(req, res) {
    upload(req,res,function(err){
        if(err){
            res.json({error_code:1,err_desc:err});
            return;
        }
        res.json({error_code:0,err_desc:null});
    });
});

Second funciton, calling executive java app

  var child = function() {
spawn('java', ['-Xms64M', '-Xms64M', '-jar', '/home/ubuntu/code/ParseExcel.jar',
            '/var/www/html/demo/test.xls']);
    child.on('close', function (exitCode) {
        if (exitCode !== 0) {
            console.error('Something went wrong!');
        }
    });
    child.stderr.on('data', function (data) {
        process.stderr.write(data);
    });
}

Is there something like angular $watch in node js that I could set it on file upload function, so if the file has been successfully upload call java function

Solution provided by @Paul (modified)

  app.post('/upload', function(req, res) {
    upload(req,res,function(err){
        if(err){
            res.json({error_code:1,err_desc:err});
            return;
        }
        // first, call your child code:
        var child = spawn('java', ['-Xms64M', '-Xms64M', '-jar', '/home/ubuntu/code/ParseExcel.jar',
            '/var/www/html/demo/test.xls']);
        child.on('close', function (exitCode) {
            if (exitCode !== 0) {
                console.error('Something went wrong!');
            }
        });
        child.stderr.on('data', function (data) {
            process.stderr.write(data);
        });
        // In my case java app parsing xls to json around 5-8 sec, that's why I'm using timeout
        setTimeout(10000);
        // then respond to the client so it's not waiting:
        res.json({error_code:0,err_desc:null});
    });
    //return req.child;
});

Answer 1

There're a lot of ways to organize your code for this, but essentially you need to call your java function inside the callback for your upload handler. Something like this should work:

 /** API path that will upload the files */
app.post('/upload', function(req, res) {
    upload(req,res,function(err){
        if(err){
            res.json({error_code:1,err_desc:err});
            return;
        }
        // first, call your child code:
        child();
        // then respond to the client so it's not waiting:
        res.json({error_code:0,err_desc:null});
    });
});