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The keystone of AJAX is the XMLHttpRequest object.
XMLHttpRequest object.
XMLHttpRequest object can be used to exchange data with a web server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.
Formula
All modern browsers (Chrome, Firefox, IE, Edge, Safari, Opera) have a built - inXMLHttpRequest object.
variable
= new XMLHttpRequest();A callback function is a function passed as a parameter to another function. In this case, the callback function should contain the code to execute when the response is ready.
xhttp.onload = function() {// What to do when the response is ready
}To send a request to a server, you can use the open() and send() methods of the
xhttp.open("GET", "ajax_info.txt");
xhttp.send();// Create an XMLHttpRequest object const xhttp = new XMLHttpRequest();
// Define a callback function xhttp.onload = function() {// Here you can use the Data
}
// Send a request xhttp.open("GET", "ajax_info.txt");
xhttp.send();For security reasons, modern browsers do not allow access across domains. This means that both the web page and the XML file it tries to load, must be located on the same server. The examples on W3Schools all open XML files located on the W3Schools domain. If you want to use the example above on one of your own web pages, the XML files you load must be located on your own server.
method, url, async, user, psw )
: the request type GET or POST url : the file location async : true (asynchronous) or false (synchronous) user : optional user name psw : optional password send()