content-type: application/x-www-form-urlencoded

When sending data to the server, use this content-type. Default is "application/x-www-form-urlencoded", which is fine for most cases. If you explicitly pass in a content-type to $.ajax() then it'll always be sent to the server (even if no data is sent). Data will always be transmitted to the server using UTF-8 charset; you must decode this appropriately on the server side.

PHP服务器，常常需要使用content-type: application/x-www-form-urlencoded请求头验证

Ajax (also AJAX /ˈeɪdʒæks/; short for "Asynchronous JavaScript and XML")[1][2] is a set of web development techniques that uses various web technologies on the client-side to create asynchronous web applications. With Ajax, web applications can send and retrieve data from a server asynchronously (in the background) without interfering with the display and behaviour of the existing page. By decoupling the data interchange layer from the presentation layer, Ajax allows web pages and, by extension, web applications, to change content dynamically without the need to reload the entire page.[3] In practice, modern implementations commonly utilize JSON instead of XML.

使用X-Requested-With: XMLHttpRequest使，将会使用Ajax技术实现，返回为json