Ok, You have instantiated XHR object and created Ready State Handler xhr.onreadystatechange = function () {.... The final step will be query resource from the server.

To do so, we need to set up the connection with OPEN method. :-

  • Specify the HTTP method (usually POST or GET) and URL of the server resources.
  • Send the request to server
xhr.open('GET', 'data1.html'); 

It is as simple as what we see above.

The open method of XHR has FIVE arguments. There are open(method, url, async, user, password). request method, request URL, , request username, and request password.

  • method - Request Method ('GET' or 'POST')
  • url - Request URL (in our case, it is just data.html. It can be verify?firstname=alex&lastname=david)
  • async - synchronous flag (if unspecified, the value is default to true, which is asynchronous. In fact, asynchronous is usually our reason to query server resource in this manner)
  • user - Request username
  • password - Request passwod

By calling OPEN method, you have only set up the connection but you have yet send anything to server.

Since we are just getting data from server, a GET request, which typically have no body, no body content parameter to send to server, we simply call send method with null argument send(null).


By now, you have seen the simplest method to query or fetch data from web server. Let's move on to see something a little bit advance.