Knowledge of XMLHttpRequest

XMLHttpRequest helps browser in transferring data between a browser and server. Without refreshing a full page, it provides a simple technique to fetch data from a server. The best part of XMLHttpRequest is that updates a part of the web page without interrupting what the user is performing.

How to use XMLHttpRequest

Following are the steps that you must follow to build AJAX applications using XMLHttpRequest-

1. Create an object of XMLHttpRequest by calling its constructor.
2. Assign a function to an event handler onreadystatechange. In the function check the value of readyState and status to obtain the response from the server.
3. Call open() method to initialize a method. In this method, specify three parameters- the type of HTTP method, URL to whom the request is to be sent, and true to call asynchronously.
4. Call send() method to send the request to the server.

var request = new XMLHttpRequest();
request.onreadystatechange = function(){
   if(this.readyState == 4 && this.status == 200){
      var response = this.responseText;
      alert(response);
   }
};
request.open("GET", "url", true);
request.send();

Properties of XMLHttpRequest

Functions of XMLHttpRequest