Detailed explanation of PHP processing Ajax requests and Ajax cross-domain issues

This article mainly introduces the relevant information on PHP's handling of Ajax requests and Ajax cross-domain issues. It is very good and has reference value. Friends in need can refer to it

PHP judgment Whether it is an Ajax request

We know that when sending an ajax request, you can create custom header information through the XMLHttpRequest object. In the jquery framework, for $ that passes it When the .ajax, $.get, or $.post method requests web page content, it will pass an HTTP_X_REQUESTED_WITH parameter to the server. In PHP, it is judged at the header layer whether it is an ajax request, and the corresponding method is based on $_SERVER[' HTTP_X_REQUESTED_WITH']Judgement. 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).

Example: The front-end page sends a normal 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 initiated JSONP cross-domain request

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

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", this indicates that what I want to request is jsonp, and a callback will be 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);
});

php backend The 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-origin 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, After any request comes, we can process and respond to it on the server side. 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:*". It means that we have enabled CORS. If you want to limit requests to only a certain domain name, you can do this:

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

Example: Requesting data across domains 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: http://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.

The above is the entire content of this article, I hope it will be helpful to everyone's study.

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