Under what circumstances will iframe cross domain?

iframe will cross domain in the following situations: 1. The domain name is different. When the source domain name of the iframe is different from the domain name of the parent page, cross-domain problems will occur; 2. The protocols are different. When the protocol of the iframe is different from the domain name of the parent page, When the protocol of the parent page is different, cross-domain problems will occur; 3. The port number is different, when the port number of the iframe is different from the port number of the parent page, cross-domain problems will occur; 4. The subdomain name is different, when the subdomain name of the iframe Cross-domain problems occur when the subdomain name of the parent page is different from that of the parent page.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

In web development, an iframe is an HTML element used to embed a web page within another web page. However, due to security reasons, browsers implement the same-origin policy, which restricts cross-domain access to iframes.

The same-origin policy is a security mechanism of the browser. It requires that web pages can only interact with resources from the same source, that is, the protocol, domain name, and port number must completely match. If the origins of two web pages are different, then the interaction between them is considered cross-origin.

Under the following circumstances, iframe will have cross-domain problems:

1. Different domain names: When the source domain name of the iframe is different from the domain name of the parent page, cross-domain problems will occur. For example, the domain name of the parent page is www.example.com, and the source domain name of the iframe is sub.example.com.

2. Different protocols: When the protocol of the iframe is different from the protocol of the parent page, cross-domain problems will occur. For example, the parent page uses https protocol, while the iframe uses http protocol.

3. Different port numbers: When the port number of the iframe is different from the port number of the parent page, cross-domain problems will occur. For example, the URL of the parent page is www.example.com:8080, and the URL of the iframe is www.example.com:3000.

4. Different subdomain names: When the subdomain name of the iframe is different from the subdomain name of the parent page, cross-domain problems will occur. For example, the domain name of the parent page is www.example.com, and the domain name of the iframe is sub.example.com.

In order to solve the cross-domain problem, you can use the following methods:

1. Use a proxy server: By setting a proxy on the server side, the cross-domain request is forwarded to the target server, and then the response is returned to client.

2. JSONP: Use JSONP (JSON with Padding) technology to send cross-domain requests to the target server by dynamically creating <script> tags, and encapsulate the response in a callback function and return it to the client. . </script>

3. CORS (Cross-Origin Resource Sharing): Set the response header on the server side to allow the specified domain name to access resources. Cross-domain resource sharing can be achieved by setting the Access-Control-Allow-Origin header on the server side.

To summarize, when the source of the iframe is different from the source of the parent page, cross-domain problems will occur. In order to solve cross-domain problems, you can use methods such as proxy servers, JSONP or CORS.

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