This is a code snippet of AJAX to call servlet and get the response from the server. Example is shown with JQuery.

AjaxCallUsingJquery.js

$(document).ready(function () {
	  //Stops the submit request
    $("#frmSomeForm").submit(function(e){
        e.preventDefault();
    });		

	  //checks for the button click event for New
	    $("#btnSubmit").click(function(e){
  
		      dataString = "somefield=" + $("#frmSomeForm #someField").val();
	        //make the AJAX request, dataType is set to json
	        //meaning we are expecting JSON data in response from the server
	        $.ajax({
	            type: "POST",
	            url: "ServletController?action=execute",
	            data: dataString,
	            cache: false,
	            dataType: "json",
	            
	            //if received a response from the server
	            success: function( data, textStatus, jqXHR) {
	                console.log("Response from ServletController " + textStatus);
	            },
	            //If there was no resonse from the server
	            error: function(jqXHR, textStatus, errorThrown){
	                 console.log("Something really bad happened " + textStatus);
	            },
	            //capture the request before it was sent to server
	            beforeSend: function(jqXHR, settings){
	                //disable the submit button until we get the response
	            },
	            //this is called after the response or error functions are finished
	            //so that we can take some action
	            complete: function(jqXHR, textStatus){
	                //enable the submit button 
	            }
	        }); //End of Ajax Call
	    }); // End of Submit button function
} // End of JQuery