About Jquery cross-origin request php Data

Why does Jquery cross-origin request php Data cause ajax failure to cross-origin requests?

Ajax itself uses the XMLHttpRequest object to interact with data. for security reasons, the browser does not allow cross-origin operations of JavaScript code, so it will warn you. Cross-origin security restrictions refer to the browser, and the server does not have cross-origin security restrictions. Therefore, two types of cross-origin solutions are derived for these two cases. one is the server side's transfer similar to the proxy method, and the other is js processing the real cross-origin access on the browser side.