How to determine if php is ajax

Today I encountered the following code in M_Controller, so I learned a little about how to judge the differences between ajax requests, post requests, REQUEST_TIME and time() functions.

define('IS_AJAX', $this->input->is_ajax_request());
define('IS_POST', $_SERVER['REQUEST_METHOD'] == 'POST' && count($_POST) ? TRUE : FALSE);
define('SYS_TIME', $_SERVER['REQUEST_TIME'] ? $_SERVER['REQUEST_TIME'] : time());

is_ajax_request() method is a method in CI to determine whether an ajax request is made. The official document explains it as: Check whether the server header contains HTTP_X_REQUESTED_WITH , returns TRUE if present, otherwise returns FALSE.

Of course, such a judgment is not perfect. The principle involved in the judgment is as follows:

When we send an ajax request through jquery, an ajax header named X-Requested-With information, the default content of the information is: XMLHttpRequest, which is the basis for the CI framework to judge ajax requests.

But how do we judge when we use native js?

xmlHttpRequest.setRequestHeader("request_type","ajax");

According to the XMLHttpRequest object, manually set the header. After the above settings are completed, we can obtain it as follows in the PHP logic code:

$_SERVER['HTTP_REQUEST_TYPE']

Obviously, the r# we set in the header ##equest_typeWhen obtaining in the background, add the prefix string of HTTP_ to obtain the Header information sent by the front desk, that is, by calling $_SERVER['HTTP_REQUEST_TYPE'] to get the header information sent by the front desk Value: ajax, of course request_type can also be set to other fields.

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