Solve the problem of PHP processing Ajax requests and Ajax cross-domain issues

PHP determines whether it is an Ajax request

We know When sending an ajax request, you can create custom header information through the XMLHttpRequest object. In the jquery framework, when requesting web content through its $.ajax, $.get, or $.post method, it A HTTP_X_REQUESTED_WITH parameter will be passed to the server. In PHP, it is judged at the header level whether it is an ajax request, and the corresponding judgment is based on $_SERVER['HTTP_X_REQUESTED_WITH']. Under normal circumstances $_SERVER['HTTP_X_REQUESTED_WITH']The default is XMLHttpRequest, $_SERVER['HTTP_X_REQUESTED_WITH'] can also be customized, using XMLHttpRequest.setRequestHeader(name, value).

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Example: The front-end page sends an ordinary ajax request to the back-end test. php.

$.ajax({
  type: "GET",
  url: 'test.php',
  success: function(data) {
    console.log(data);
  }
});

The server test.php can determine whether the request is an Ajax asynchronous request, and then respond according to business needs.

The following is the code to simply verify whether the server test.php is an ajax request:

function isAjax() {
  return @$_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest' ? true : false;
}
if (isAjax()) {
  echo 'Ajax Request Success.';
} else {
  echo 'No.';
}

Ajax initiates a JSONP cross-domain request

We can implement cross-domain ajax requests through jQuery's JSONP method, and the server-side PHP also needs to handle it accordingly, which means that the PHP side must request and return data in a certain format with the front-end page.

Example: The front-end page initiates a JSONP request:

$.ajax({
  type: "get",
  data: "random="+Math.random(),
  url: "http://demo.jb51.net/phpajax/jsonp.php",
  dataType: "jsonp",
  jsonp: "callback",
  success: function(data) {
   console.log(data);
  },
  error: function() {
   console.log('Request Error.');
  }
});

We will find that the ajax request parameters include dataType: "jsonp" and jsonp: "callback", which indicates what I want to request. It is jsonp, and there will be a callback callback returned. Of course, we can also customize the callback function, such as jsonpCallback:"success_jsonpCallback"

It can also be simply written as:

jQuery.getJSON('http://demo.jb51.net/phpajax/jsonp.php?callback=?",{
 random: Math.random()
}, function(data){
 console.log(data);
});

The php back-end service code can be written like this (note the format of the output return) :

$data = array(
  'rand' => $_GET['random'],
  'msg' => 'Success'
);
echo $_GET['callback'].'('.json_encode($data).')';

Ajax cross-domain request: CORS

##CORS, also known as cross-domain resource sharing, the full English name is Cross-Origin Resource Sharing. Suppose we want to use Ajax to request data from the page of a.com to the page of b.com. Usually, due to the same-origin policy, this kind of request is not allowed, and the browser will also return a "source mismatch" error. Hence the term “cross-domain”. But we also have a solution. We can add a line of code to the header information of the page on b.com:

header("Access-Control-Allow-Origin: *");

When the header we set is the above information, we can process any request on the server side after it comes. and response, then you can see its header information settings in the debugging tool. One of the pieces of information in the red box is "*Access-Control-Allow-Origin: *", which means that we have enabled CORS. If you want to restrict only certain A request for a domain name can be like this:

header("Access-Control-Allow-Origin: https://www.jb51.net");

Example: Cross-domain request data through CORS

$.ajax({
  type: "get",
  data: "random="+Math.random(),
  url: "http://demo.jb51.net/phpajax/ajax.php",
  dataType: "json",
  success: function(data) {
    console.log(data);
    $("#result_3").html(data.msg+':'+data.rand);
  },
  error: function() {
   $("#result_3").html('Request Error.');
  }
});

We add this code to ajax.php under another website domain name:

header("Access-Control-Allow-Origin: https://www.jb51.net");
$data = array(
  'rand' => $_GET['random'],
  'msg' => 'Success'
);
echo json_encode($data);

This enables a cross-domain asynchronous request to be initiated from the www.jb51.net page to the domain name path demo.jb51.net/phpajax/ajax.php, and a response is obtained.

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