Loading cross-domain endpoint with AJAX

Question

jQuery Ajax Notes

• Due to browser security restrictions, most Ajax requests are subject to the same origin policy; the request can not successfully retrieve data from a different domain, subdomain, port, or protocol.
• Script and JSONP requests are not subject to the same origin policy restrictions.

There are some ways to overcome the cross-domain barrier:

• CORS Proxy Alternatives
• Ways to circumvent the same-origin policy
• Breaking The Cross Domain Barrier

There are some plugins that help with cross-domain requests:

• Cross Domain AJAX Request with YQL and jQuery
• Cross-domain requests with jQuery.ajax

Heads up!

The best way to overcome this problem, is by creating your own proxy in the back-end, so that your proxy will point to the services in other domains, because in the back-end not exists the same origin policy restriction. But if you can't do that in back-end, then pay attention to the following tips.

---

**Warning!**

Using third-party proxies is not a secure practice, because they can keep track of your data, so it can be used with public information, but never with private data.

---

The code examples shown below use jQuery.get() and jQuery.getJSON(), both are shorthand methods of jQuery.ajax()

---

CORS Anywhere

2021 Update

Public demo server (cors-anywhere.herokuapp.com) will be very limited by January 2021, 31st

The demo server of CORS Anywhere (cors-anywhere.herokuapp.com) is meant to be a demo of this project. But abuse has become so common that the platform where the demo is hosted (Heroku) has asked me to shut down the server, despite efforts to counter the abuse. Downtime becomes increasingly frequent due to abuse and its popularity.

To counter this, I will make the following changes:

1. The rate limit will decrease from 200 per hour to 50 per hour.
2. By January 31st, 2021, cors-anywhere.herokuapp.com will stop serving as an open proxy.
3. From February 1st. 2021, cors-anywhere.herokuapp.com will only serve requests after the visitor has completed a challenge: The user (developer) must visit a page at cors-anywhere.herokuapp.com to temporarily unlock the demo for their browser. This allows developers to try out the functionality, to help with deciding on self-hosting or looking for alternatives.

---

CORS Anywhere is a node.js proxy which adds CORS headers to the proxied request.
To use the API, just prefix the URL with the API URL. (Supports https: see github repository)

If you want to automatically enable cross-domain requests when needed, use the following snippet:

$.ajaxPrefilter( function (options) {
  if (options.crossDomain && jQuery.support.cors) {
    var http = (window.location.protocol === 'http:' ? 'http:' : 'https:');
    options.url = http + '//cors-anywhere.herokuapp.com/' + options.url;
    //options.url = "http://cors.corsproxy.io/url=" + options.url;
  }
});

$.get(
    'http://en.wikipedia.org/wiki/Cross-origin_resource_sharing',
    function (response) {
        console.log("> ", response);
        $("#viewer").html(response);
});

---

Whatever Origin

Whatever Origin is a cross domain jsonp access. This is an open source alternative to anyorigin.com.

To fetch the data from google.com, you can use this snippet:

// It is good specify the charset you expect.
// You can use the charset you want instead of utf-8.
// See details for scriptCharset and contentType options: 
// http://api.jquery.com/jQuery.ajax/#jQuery-ajax-settings
$.ajaxSetup({
    scriptCharset: "utf-8", //or "ISO-8859-1"
    contentType: "application/json; charset=utf-8"
});

$.getJSON('http://whateverorigin.org/get?url=' + 
    encodeURIComponent('http://google.com') + '&callback=?',
    function (data) {
        console.log("> ", data);

        //If the expected response is text/plain
        $("#viewer").html(data.contents);

        //If the expected response is JSON
        //var response = $.parseJSON(data.contents);
});

---

CORS Proxy

CORS Proxy is a simple node.js proxy to enable CORS request for any website. It allows javascript code on your site to access resources on other domains that would normally be blocked due to the same-origin policy.

• CORS-Proxy gr2m
• CORS-Proxy rmadhuram

How does it work? CORS Proxy takes advantage of Cross-Origin Resource Sharing, which is a feature that was added along with HTML 5. Servers can specify that they want browsers to allow other websites to request resources they host. CORS Proxy is simply an HTTP Proxy that adds a header to responses saying "anyone can request this".

This is another way to achieve the goal (see www.corsproxy.com). All you have to do is strip http:// and www. from the URL being proxied, and prepend the URL with www.corsproxy.com/

$.get(
    'http://www.corsproxy.com/' +
    'en.wikipedia.org/wiki/Cross-origin_resource_sharing',
    function (response) {
        console.log("> ", response);
        $("#viewer").html(response);
});

---

CORS proxy browser

Recently I found this one, it involves various security oriented Cross Origin Remote Sharing utilities. But it is a black-box with Flash as backend.

You can see it in action here: CORS proxy browser
Get the source code on GitHub: koto/cors-proxy-browser

You can use Ajax-cross-origin a jQuery plugin. With this plugin you use jQuery.ajax() cross domain. It uses Google services to achieve this:

The AJAX Cross Origin plugin use Google Apps Script as a proxy jSON getter where jSONP is not implemented. When you set the crossOrigin option to true, the plugin replace the original url with the Google Apps Script address and send it as encoded url parameter. The Google Apps Script use Google Servers resources to get the remote data, and return it back to the client as JSONP.

It is very simple to use:

    $.ajax({
        crossOrigin: true,
        url: url,
        success: function(data) {
            console.log(data);
        }
    });

You can read more here: http://www.ajax-cross-origin.com/

If the external site doesn't support JSONP or CORS, your only option is to use a proxy.

Build a script on your server that requests that content, then use jQuery ajax to hit the script on your server.

Just put this in the header of your PHP Page and it ill work without API:

header('Access-Control-Allow-Origin: *'); //allow everybody  

or

header('Access-Control-Allow-Origin: http://codesheet.org'); //allow just one domain 

or

$http_origin = $_SERVER['HTTP_ORIGIN'];  //allow multiple domains

$allowed_domains = array(
  'http://codesheet.org',
  'http://stackoverflow.com'
);

if (in_array($http_origin, $allowed_domains))
{  
    header("Access-Control-Allow-Origin: $http_origin");
}