在AJAX和Node.js中使用发布请求时，将结果保存在JSON文件中

Question

Now I am writing an javascript to track the system configuration of users eg screen resolution statistic. I first wrote the AJAX file to collection in object form and use node.js to take the request and finally write the input into the json file in server side.

My AJAX code is as follows:

  try{

  window.onload = function(url, callback, data, x) {
  var sWidth = screen.width;
  var sHeight = screen.height;
  var sColor = screen.colorDepth;
  var sPlatform = window.navigator.platform;
  var sLanguage = navigator.language;
  var sTimeZone = Intl.DateTimeFormat().resolvedOptions().timeZone;

  var info = {
    width: sWidth,
    height: sHeight,
    color: sColor,
    platform: sPlatform,
    language: sLanguage,
    timezone: sTimeZone
  };

    //var http = new XMLHttpRequest();
    var http = new(this.XMLHttpRequest || ActiveXObject)('MSXML2.XMLHTTP.3.0');

    http.onreadystatechange = function () {
      if (http.readyState == 4 && http.status == 200) {
        console.log(JSON.parse(http.response));
      }
    };

    http.open("POST", "http://127.0.0.1:8080/ReturnFingerprint.json", true);
    http.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
    http.setRequestHeader("Content", "application/x-www-form-urlencoded")
    http.send(info);
  }
} catch (e) {
  console.log(e);
}

And the following Node.js code to take over the AJAX request

var express = require('express');
var bodyParser = require('body-parser');
var app= express();
var urlencodedParser = bodyParser.urlencoded({ extended: false })

app.use(bodyParser.json());
app.options('/Fingerprint', cors()) ;

app.post('/Fingerprint', urlencodedParser, function(req, res, next) {
  if (!req.body) {
    var json = JSON.stringify(req.body);
    var fs = require('fs');
    fs.readFile('ReturnFingerprint.json', 'utf8', function readFileCallback(err, data){
    if (err){
        console.log(err);
        next(err)
    } else {
      data = JSON.parse(data);
      json = JSON.stringify(data);
      fs.writeFile('ReturnFingerprint.json', json, 'utf8', function writeFilecallback (err, data) {
        res.json(json)});
      });
    }
  }
  res.json(json);
});

When I checked the json file, there is nth updated.

And when I inspected the network element in google chrome, it returns that the ReturnFingerprint.json is pending and no more error message or detail is provided.

What is the error of the code?Many thanks for your help in advance.

Answer 1

You need to tell Express that you're done with handling of the request eg. by res.send('hello') or res.json(jsonObject) . You should call it in the writeFile callback.