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:
There are some plugins that help with cross-domain requests:
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:
- The rate limit will decrease from 200 per hour to 50 per hour.
- By January 31st, 2021, cors-anywhere.herokuapp.com will stop serving as an open proxy.
- 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.
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);
});
The http://www.corsproxy.com/ domain now appears to be an unsafe/suspicious site. NOT RECOMMENDED TO USE.
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
