Node.Js error "No 'Access-Control-Allow-Origin' header is present on the requested"

Question

This question is similar to others; however there is a difference that makes it very confusing why it is not working.

My JavaScript was calling 6 json files and all worked correctly. In Node.JS I have cors and headers set up as shown below:

var fs = require('fs');
var http = require("https");
var express = require('express');
var app = express();
var path = require('path');
var http = require("http");
var url = require("url");
var req = require('request')
var pem = require('pem');
var cors = require("cors");

app.use(express.static(path.join(__dirname, '../')));

app.listen(process.env.PORT || 8080);

app.options('*', cors()); 

app.use(function(req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-  With, Content-Type, Accept");
    next();   
});

app.all('/posts', function(req, res){
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
});

app.get('/', function (req, res) { 
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept"); 
    res.writeHead(200, {'Content-Type': 'text/plain'});
    contents = fs.readFileSync("sliderImages.json", "utf8");
    console.log(path.join(__dirname, '/sliderImages.json'));
    res.end(contents);
});

All 6 json files are grabbed from the absolute URL path by Node JS. I have made 2 more yesterday and everything was working fine. However, today I made one and implemented the same way and received the following error:

No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access.

I am implementing each the same way, example:

var base_url = 'http://127.0.0.1:8080';

mainInformationTop();

function mainInformationTop()
{
    $.ajax({
        type: "GET", 
        url: base_url + "/api/topInformation.json", 
        dataType: "json",
        success: function(response)
        {
            var json_obj = response.mainDescription;
            var imagesSlider="";
            var imagesSliderDescription ="";
            for (var i = 0; i< json_obj.length; i++) 
            {

            }

        }
        , 
        error: function(jqXHR, textStatus, errorThrown) {
            alert(jqXHR.status);
        }  
    })    
}

I don't think the json file is relevant but below is my json file:

{"mainDescription":[
{
"display": "my display",
"description" : "my description"
}
]}

I have took out the information in the for loop for testing as well as my append because irrelevant. For some reason it fails and goes to error instead of success. All other calls are set up the same way and work correctly.

Answer 1

This is a much more simple version of this answer which achieves the same effect:

var fs = require('fs');
var express = require('express');
var cors = require('cors');

var app = express();

app.use(cors()); 
app.use(express.static(path.join(__dirname, '../')));

app.get('/', function (req, res) { 
  res.writeHead(200, {'Content-Type': 'text/plain'});
  contents = fs.readFileSync('sliderImages.json', 'utf8');
  res.end(contents);
});

app.listen(process.env.PORT || 8080);

Answer 2

Fixed it.

var fs = require('fs');
var http = require("https");
var express = require('express');
var app = express();
var path = require('path');
var http = require("http");
var url = require("url");
var req = require('request')
var pem = require('pem');
var cors = require("cors");

app.use(function(req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});
app.use(express.static(path.join(__dirname, '../')));

app.listen(process.env.PORT || 8080);

app.options('*', cors()); 

app.all('/*', function (req, res, next) {
    res.header("Access-Control-Allow-Origin", "http://localhost:8080");
    res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
    res.header("Access-Control-Allow-Headers", "X-Requested-With,     Content-Type");
    next();
});

app.get('/', function (req, res) { 
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept"); 
    res.writeHead(200, {'Content-Type': 'text/plain'});
    contents = fs.readFileSync("sliderImages.json", "utf8");
    console.log(path.join(__dirname, '/sliderImages.json'));
    res.end(contents);
 });

Despite what the comments said the only real thing I changed was moving the app.use before everything else. This solved the issue.

Answer 3

Install cors

npm install cors --save

Write this code in your app.js

const cors = require('cors');
const express = require('express');
let app = express();
app.use(cors());
app.options('*', cors()); //put this before your route 

Answer 4

I also suffer this problem the code was as same as above but we want to put the code in starting point. dont put this code in last that means before (res.end()) sending response to client. Three methods (GET,POST,HEAD) that allowed you when you put this code anywhere i think but for other method try this and try with other modules like cors,express but i used http module only

var server=http.createServer(function (req, res) {

res.setHeader("Access-Control-Allow-Origin","*");
res.setHeader("Access-Control-Allow-Methods","PUT,GET,DELETE,PATCH")
res.setHeader('Access-Control-Allow-Credentials', true)
res.setHeader('Access-Control-Allow-Headers','X-Requested-With,content-type,Origin,Accept,Authorization')
// your other code followes