No 'Access-Control-Allow-Origin' - Node / Apache Port Issue

Try adding the following middleware to your NodeJS/Express app (I have added some comments for your convenience):

// Add headers before the routes are defined
app.use(function (req, res, next) {

    // Website you wish to allow to connect
    res.setHeader('Access-Control-Allow-Origin', 'http://localhost:8888');

    // Request methods you wish to allow
    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');

    // Request headers you wish to allow
    res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type');

    // Set to true if you need the website to include cookies in the requests sent
    // to the API (e.g. in case you use sessions)
    res.setHeader('Access-Control-Allow-Credentials', true);

    // Pass to next layer of middleware
    next();
});

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Accepted answer is fine, in case you prefer something shorter, you may use a plugin called cors available for Express.js

It's simple to use, for this particular case:

var cors = require('cors');

// use it before all route definitions
app.use(cors({origin: 'http://localhost:8888'}));

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Another way, is simply add the headers to your route:

router.get('/', function(req, res) {
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE'); // If needed
    res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type'); // If needed
    res.setHeader('Access-Control-Allow-Credentials', true); // If needed

    res.send('cors problem fixed:)');
});

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The top answer worked fine for me, except that I needed to whitelist more than one domain.

Also, top answer suffers from the fact that OPTIONS request isn't handled by middleware and you don't get it automatically.

I store whitelisted domains as allowed_origins in Express configuration and put the correct domain according to origin header since Access-Control-Allow-Origin doesn't allow specifying more than one domain.

Here's what I ended up with:

var _ = require('underscore');

function allowCrossDomain(req, res, next) {
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');

  var origin = req.headers.origin;
  if (_.contains(app.get('allowed_origins'), origin)) {
    res.setHeader('Access-Control-Allow-Origin', origin);
  }

  if (req.method === 'OPTIONS') {
    res.send(200);
  } else {
    next();
  }
}

app.configure(function () {
  app.use(express.logger());
  app.use(express.bodyParser());
  app.use(allowCrossDomain);
});

---

The answer code allow only to localhost:8888. This code can't be deployed to the production, or different server and port name.

To get it working for all sources, use this instead:

// Add headers
app.use(function (req, res, next) {

    // Website you wish to allow to connect
    res.setHeader('Access-Control-Allow-Origin', '*');

    // Request methods you wish to allow
    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');

    // Request headers you wish to allow
    res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type');

    // Set to true if you need the website to include cookies in the requests sent
    // to the API (e.g. in case you use sessions)
    res.setHeader('Access-Control-Allow-Credentials', true);

    // Pass to next layer of middleware
    next();
});

---

Install cors dependency in your project:

npm i --save cors

Add to your server configuration file the following:

var cors = require('cors');
app.use(cors());

It works for me with 2.8.4 cors version.

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Hi this happens when the front end and backend is running on different ports. The browser blocks the responses from the backend due to the absence on CORS headers. The solution is to make add the CORS headers in the backend request. The easiest way is to use cors npm package.

var express = require('express')
var cors = require('cors')
var app = express()
app.use(cors())

This will enable CORS headers in all your request. For more information you can refer to cors documentation

https://www.npmjs.com/package/cors

---

This worked for me.

app.get('/', function (req, res) {

    res.header("Access-Control-Allow-Origin", "*");
    res.send('hello world')
})

You can change * to fit your needs. Hope this can help.

---

All the other answers didn't work for me. (including cors package, or setting headers through middleware)

For socket.io 3^ this worked without any extra packages.

const express = require('express');
const app = express();

const server = require('http').createServer(app);
const io = require('socket.io')(server, {
    cors: {
        origin: "*",
        methods: ["GET", "POST"]
    }
});

---

app.all('*', function(req, res,next) {
    /**
     * Response settings
     * @type {Object}
     */
    var responseSettings = {
        "AccessControlAllowOrigin": req.headers.origin,
        "AccessControlAllowHeaders": "Content-Type,X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,  Date, X-Api-Version, X-File-Name",
        "AccessControlAllowMethods": "POST, GET, PUT, DELETE, OPTIONS",
        "AccessControlAllowCredentials": true
    };

    /**
     * Headers
     */
    res.header("Access-Control-Allow-Credentials", responseSettings.AccessControlAllowCredentials);
    res.header("Access-Control-Allow-Origin",  responseSettings.AccessControlAllowOrigin);
    res.header("Access-Control-Allow-Headers", (req.headers['access-control-request-headers']) ? req.headers['access-control-request-headers'] : "x-requested-with");
    res.header("Access-Control-Allow-Methods", (req.headers['access-control-request-method']) ? req.headers['access-control-request-method'] : responseSettings.AccessControlAllowMethods);

    if ('OPTIONS' == req.method) {
        res.send(200);
    }
    else {
        next();
    }


});

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Add following code in app.js of NODEJ Restful api to avoid "Access-Control-Allow-Origin" error in angular 6 or any other framework

var express = require('express');
var app = express();

var cors = require('cors');
var bodyParser = require('body-parser');

//enables cors
app.use(cors({
  'allowedHeaders': ['sessionId', 'Content-Type'],
  'exposedHeaders': ['sessionId'],
  'origin': '*',
  'methods': 'GET,HEAD,PUT,PATCH,POST,DELETE',
  'preflightContinue': false
}));

---

You could use cors package to handle it.

var cors = require('cors')
var app = express()

app.use(cors())

for setting the specific origin

app.use(cors({origin: 'http://localhost:8080'}));

know more

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You can use "$http.jsonp"

OR

Below is the work around for chrome for local testing

You need to open your chrome with following command. (Press window+R)

Chrome.exe --allow-file-access-from-files

Note : Your chrome must not be open. When you run this command chrome will open automatically.

If you are entering this command in command prompt then select your chrome installation directory then use this command.

Below script code for open chrome in MAC with "--allow-file-access-from-files"

set chromePath to POSIX path of "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" 
set switch to " --allow-file-access-from-files"
do shell script (quoted form of chromePath) & switch & " > /dev/null 2>&1 &"

second options

You can just use open(1) to add the flags: open -a 'Google Chrome' --args --allow-file-access-from-files

---

/** * Allow cross origin to access our /public directory from any site. * Make sure this header option is defined before defining of static path to /public directory */ expressApp.use('/public',function(req, res, next) { res.setHeader("Access-Control-Allow-Origin", "*"); // Request headers you wish to allow res.setHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept"); // Set to true if you need the website to include cookies in the requests sent res.setHeader('Access-Control-Allow-Credentials', true); // Pass to next layer of middleware next(); }); /** * Server is about set up. Now track for css/js/images request from the * browser directly. Send static resources from "./public" directory. */ expressApp.use('/public', express.static(path.join(__dirname, 'public'))); If you want to set Access-Control-Allow-Origin to a specific static directory you can set the following.

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Apart from all listed answers, I had the same error

I have both access to frontend and backend, I already added cors module app.use(cors()); Still, I was struggling with this error.

After some debugging, I found the issue. When I upload a media which size was more than 1 MB then the error was thrown by Nginx server

<html>

<head>
    <title>413 Request Entity Too Large</title>
</head>

<body>
    <center>
        <h1>413 Request Entity Too Large</h1>
    </center>
    <hr>
    <center>nginx/1.18.0</center>
</body>

</html>

But in the console of frontend, I found the error

Access to XMLHttpRequest at 'https://api.yourbackend.com' from origin 'https://web.yourfromntend.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

So It makes confusion here. But the route cause of this error was from nginx configuration. It's just because the directive client_max_body_size value has been set to 0 by default. It determines what the allowable HTTP request size can be is client_max_body_size. This directive may already be defined in your nginx.conf file located at /etc/nginx/nginx.conf Now you need to add/edit the value of the directive client_max_body_size either at http or server.

server {
    client_max_body_size 100M;
    ...
}

Once you have set your desired value, save your changes and reload Nginx: service nginx reload

After these changes, It's working well

REFERENCE: https://www.keycdn.com/support/413-request-entity-too-large#:~:text=%23,processed%20by%20the%20web%20server.&text=An%20example%20request%2C%20that%20may,e.g.%20a%20large%20media%20file).

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