XML HttpRequest
All modern browsers have a built-in XMLHttpRequest object to
request data from a server.
The XMLHttpRequest Object
The XMLHttpRequest object can be used to request data from a web server.
The XMLHttpRequest object is a developers dream, because you can:
Update a web page without reloading the page
Request data from a server - after the page has loaded
Receive data from a server - after the page has loaded
Send data to a server - in the background
XMLHttpRequest Example
When you type a character in the input field below, an XMLHttpRequest is sent to the server,
and some name suggestions are returned
(from the server):
Example
Start typing a name in the input field below:
Name:
Suggestions:
The example above is explained in the AJAX chapters of this tutorial.
Sending an XMLHttpRequest
A common JavaScript syntax for using the XMLHttpRequest object looks much like this:
Example
var xhttp = new XMLHttpRequest();xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
// Typical action to be performed when the document is ready:
document.getElementById("demo").innerHTML = xhttp.responseText;
}};
xhttp.open("GET", "filename", true);
xhttp.send();
Try it Yourself »
Example Explained
The first line in the example above creates an XMLHttpRequest
object:
var xhttp = new XMLHttpRequest();
The onreadystatechange property specifies a function to be executed
every time the status of the XMLHttpRequest object changes:
xhttp.onreadystatechange = function()
When readyState property is 4 and the status
property is 200, the response is ready:
if (this.readyState == 4 && this.status == 200)
The responseText property returns the server response as a
text string.
The text string can be used to update a web page:
document.getElementById("demo").innerHTML = xhttp.responseText;
You will learn a lot more about the XMLHttpRequest object in the AJAX chapters of this tutorial.
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Reference: https://www.w3schools.com/xml/xml_http.asp