Questions frequently asked by front-end interviewers: How to handle cross-domain requests?

Cross-domain requests are a common topic in front-end interviews and one of the questions often asked by interviewers. In modern website development, the front-end and back-end are usually not in the same domain, so cross-domain requests are particularly important. When handling cross-domain requests, front-end developers need to master some basic knowledge and skills to ensure data security and reliability. This article will introduce in detail what cross-domain requests are, the causes of cross-domain requests, and how to handle cross-domain requests. We hope to help readers better understand and deal with issues related to cross-domain requests.

First of all, let us understand what a cross-domain request is. Simply put, cross-domain request refers to the situation where the source of the current page (protocol, domain name, port number) of the network request initiated by the browser is inconsistent with the source of the requested resource. Cross-domain requests are involved when the front-end page requests resources from different sources. The cause of cross-origin requests is primarily the browser's same-origin policy, which restricts how a document or script loaded from one source by a page can interact with resources from another source. This is to protect user privacy and security and prevent malicious websites from stealing data.

So, how to handle cross-domain requests? Below we will introduce several common cross-domain request processing methods:

1. JSONP (JSON with Padding): JSONP is a solution for cross-domain requests. It implements cross-domain requests by dynamically adding <script></script> tags. Dynamically create a <script></script> tag on the client side, with its src attribute pointing to the server address with the callback function. The data returned by the server will be executed as JavaScript, thereby realizing cross-domain requests. However, it should be noted that JSONP only supports GET requests, has security issues, and is vulnerable to XSS attacks.
2. CORS (Cross-Origin Resource Sharing): CORS is an official standard cross-domain solution that enables cross-domain requests by setting response headers on the server side. You need to set the Access-Control-Allow-Origin allowed domain name in the response header, as well as other related header information. CORS supports complex requests (such as PUT, DELETE, etc.) and does not have security issues like JSONP. It is currently the recommended cross-domain solution.
3. Proxy: By setting up a proxy on your own server, you can forward front-end requests to the back-end interface to implement cross-domain requests. When the front-end requests its own server interface, the server then requests the real target interface and then returns the response to the front-end. The proxy method is suitable for complex cross-domain scenarios, but you need to maintain a proxy server yourself.
4. WebSocket: WebSocket is a protocol for full-duplex communication over a single TCP connection and is not subject to the same-origin policy. The front end can establish a persistent connection with the server through WebSocket for cross-domain communication. However, it should be noted that the WebSocket interface is different from the traditional HTTP interface and requires corresponding support from the backend.

In summary, there are many ways to handle cross-domain requests, and choosing the appropriate method depends on specific business scenarios and needs. In actual development, you can choose an appropriate cross-domain solution based on specific circumstances and follow relevant security specifications to ensure the safety and reliability of data transmission.

Interviewers often ask how to handle cross-domain requests, which also tests front-end developers’ understanding and practical experience of website security and performance optimization. For front-end developers, mastering the basic principles and common solutions of cross-domain requests can effectively deal with issues related to cross-domain requests and improve their comprehensive capabilities and competitiveness. I hope this article can help readers better understand and master the relevant knowledge of cross-domain request processing, and provide help for future interviews and jobs.

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