How JavaScript sets cookies across domains

JavaScript is a widely used scripting language that is widely used in web development. It allows developers to add various dynamic effects and interactive functions to web pages in an interactive way. But with the development of web applications, cross-domain problems have become more and more common. In this article, we will learn how JavaScript sets cookies across domains.

What is cross-domain?

Cross-domain refers to the problem that occurs when the JavaScript code of a website attempts to access pages from different sources (protocols, domain names, ports) in the same browser. For security reasons, browsers prohibit cross-domain requests.

Why set cookies?

Cookies are small pieces of text used by websites, stored in an area on the user's computer, and sent by the browser to the server. Cookies can store login credentials, shopping cart information, etc.

Consider the following scenario: You are developing a web application that requires users to log in before they can access specific pages. You may use cookies to store login information and ensure that only logged-in users can access protected pages. However, if the protected page is loaded from a different source, the cookie must be set across domains in order for it to access the cookies.

How to set cookies across domains?

A typical cookie setting code may be similar to the following code:

document.cookie = 'key=value;domain=example.com;expires=Sat, 01 Jan 2050 00:00:00 GMT;path=/'

However, due to the restrictions of the same origin policy, if the current page is not the same source as the page where the cookie should be set, it will not succeed. Set cookies.

One of the solutions is to use JSONP (JSON with Padding). JSONP uses script tags to provide special cases for cross-domain access. For example, the following code can be added to the login page:

<script src="http://example.com/setCookie?callback=callback"></script>

The setCookie file should return a JavaScript callback function that will be called on the same page where the script tag is added, allowing you to successfully set the cookie.

Another solution is to use a proxy. Most servers support HTTP proxy servers. Using a proxy, a web application can send a proxy request to the server in order to access cookies on another domain. This method involves sending proxy requests to a proxy server, which is then responsible for sending the request to the target server, thus solving cross-domain issues.

Finally, some browsers support setting CORS (Cross Resource Sharing) headers, which instruct the browser to accept requests from other domains. Before setting cookies via CORS, make sure you read the specifications for cross-origin resource sharing.

Summary

Setting cookies across domains with JavaScript can be an important issue in web development, and in some cases may be restricted by the same-origin policy. At this point, we can use JSONP, proxies, or CORS to set cookies across domains. Either way, safety must be ensured. Web developers can choose a solution that suits them during actual development.

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