node.js formidable使用上传的文件URL生成变量

Question

嗨我使用node和formidable提交表单中的文件，这个文件的URL我需要保存在一个全局变量中以便以后使用它与WATSON IBM图像识别api。

我是节点的新手，所以我卡住了，变量名是newpath，我能够在提交表单后打印它，但以后无法访问变量。

我一定做错了，如果你能指出我的错误，我真的很感激。

const http = require('http');
var formidable = require('formidable');

const hostname = '127.0.0.1';
const port = 3500;

var fs = require('fs');

/// WATSON

var VisualRecognitionV3 = require('watson-developer-cloud/visual-recognition/v3');
var visualRecognition = new VisualRecognitionV3({
  version: '2018-03-19',
  iam_apikey: 'xxxxxxx'
});

// SERVER AND FORM

const server = http.createServer((req, res) => {

  if (req.url == '/fileupload') {
    var form = new formidable.IncomingForm();
    form.parse(req, function (err, fields, files) {
      var oldpath = files.filetoupload.path;
      var newpath = '/users/myuser/coding/visualr/' + files.filetoupload.name;

      fs.rename(oldpath, newpath, function (err) {
        if (err) throw err;
        res.write('File uploaded and moved!');
        // this is the path, variable newpath, but can't be accessed
        // outside this function, tried to make it global but didn't work either

        res.write('newpath');
        res.end();
      });


 });

  } else {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
    res.write('<input type="file" name="filetoupload"><br>');
    res.write('<input type="submit">');
    res.write('</form>');
    return res.end();
  }
  });


 var images_file = fs.createReadStream(newpath);
// I want to put the variable newpath in this function: but it doesn't work...

var params = {
  images_file: images_file,
};

visualRecognition.classify(params, function(err, response) {
  if (err)
    console.log(err);
  else
    console.log(JSON.stringify(response, null, 2))
});


// ENDS

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

Answer 1

变量是在if (req.url == '/fileupload') {...}块的上下文中定义的，因此它不会在该块之外可用。

要在代码中的任何位置使用变量，请在createServer块之外定义它：

var newpath; // this variable will have global context for this file

const server = http.createServer((req, res) => {

  if (req.url == '/fileupload') {
    var form = new formidable.IncomingForm();
    form.parse(req, function (err, fields, files) {
      var oldpath = files.filetoupload.path;

      // set the variable to its intended value here
      newpath = '/users/myuser/coding/visualr/' + files.filetoupload.name;

      fs.rename(oldpath, newpath, function (err) {
        if (err) throw err;
        res.write('File uploaded and moved!');
        res.write('newpath');
        res.end();
      });
    });
  } else {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
    res.write('<input type="file" name="filetoupload"><br>');
    res.write('<input type="submit">');
    res.write('</form>');
    return res.end();
  }
});

console.log(newpath); // the variable should be available here, because of its context