Javascript cross domain

In js, when we directly request data on different domains with XMLHttpRequest, it is not possible. However, it is possible to introduce js script files on different domains on the page, and jsonp uses this feature to achieve it.

Explain in detail the js cross-domain problem
https://segmentfault.com/a/1190000000718840

Talk about JSON and JSONP, maybe you will be enlightened, including jQuery use case
http://www.cnblogs.com/dowinning/archive/2012/04/19 /json-jsonp-jquery.htmlWhat

is JS cross-domain access?
https://www.zhihu.com/question/26376773/answer/32736193