Cross-domain details

What is a cross-domain
JavaScript is not allowed to invoke objects of other pages across domains for security reasons. But the security restrictions also bring a lot of trouble to inject IFRAME or AJAX applications. Here are some simple things to sort out about cross-domain issues:

First what is cross-domain, simple to understand is because of the JavaScript homologous policy limitations, a.com domain name JS can not operate B.Com or c.a.com under the domain name of the object. A more detailed explanation can be seen in the following table:
URL description whether to allow communication
Http://www.a.com/a.js
Http://www.a.com/b.js allowed under the same domain name
Http://www.a.com/lab/a.js
http://www.a.com/script/b.js different folders under the same domain name allow
Http://www.a.com:8000/a.js
Http://www.a.com/b.js the same domain name, different ports are not allowed
Http://www.a.com/a.js
Https://www.a.com/b.js the same domain name, different protocols not allowed
Http://www.a.com/a.js
Http://70.32.92.74/b.js domain and domain name corresponding IP is not allowed
Http://www.a.com/a.js
Http://script.a.com/b.js primary domain, different subdomains are not allowed
Http://www.a.com/a.js
Http://a.com/b.js the same domain name, different level two domain names (IBID.) are not allowed (cookies are not allowed in this case)
Http://www.cnblogs.com/a.js
Http://www.a.com/b.js different domain names are not allowed

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Ajax or an IFRAME points to an address where the level two domain name, port, and protocol must be exactly the same as the main page, or even cross-domain
Like what a.baidu.com访问b.baidu.com 是跨域； a.baidu.com:8080访问a.baidu.com:80 是跨域； http://a.baidu.com访问https://a.baidu.com 是跨域Cross-domain refers to a resource that requests another domain name from a Web page of a domain name. For example, from the http://www.baidu.com/page to requesthttp://www. google.com of resources. The strict definition of cross-domain is that as long as the protocol, the domain name, the port has any difference, it is considered to be a cross-domain.
How to achieve cross-domain fetch data, LS said JSONP is the most common, you can refer to this article cross-domain and cross-domain access

Cross-domain details