JQuery Ajax cross-domain access solution_jquery

The specific situations are:
1. Mutual access between this domain and sub-domains: http://www.aa.com/ and book.aa.com
2. Mutual access between this domain and other domains: http:/ /www.aa.com/ and http://www.bb.com/ use iframe
3. Mutual access between this domain and other domains: http://www.aa.com/ and http://www .bb.com/ Use XMLHttpRequest to access the proxy
4. Mutual access between this domain and other domains: http://www.aa.com/ and http://www.bb.com/ Use JS to create dynamic scripts
Today we will mainly discuss the 4th solution. The difference between this and the previous one is that the request is made using the