Client-Server call in ServiceNow / Ajax Call / Asynchronous Call

 AJAX (asynchronous JavaScript and XML) is a group of interrelated, client-side development techniques used to create asynchronous Web applications.

AJAX enables web applications to send and retrieve information to and from a server in the background, without impacting the user experience with the displayed web page.

GlideAjax:

The GlideAjax class allows the execution of server-side code from the client. GlideAjaxcalls pass parameters to the script includes, and, using naming conventions, allows the use of these parameters.

Using GlideAjax:

·         Initialize GlideAjax with the name of the script include that you want to use.

·         When creating the script include, you must set the name field to be exactly the same as the class name.

·         When creating the script include, you must select the Client callable check box.

·         Specify the parameter sysparm_name. GlideAjax uses sysparm_name to find which function to use.

·         Any extra parameters may be passed in, all of which must begin with sysparm_. Avoid using predefined parameter names:

o   sysparm_name

o   sysparm_function

o   sysparm_value

o   sysparm_type

·         Code is then executed with the getXML() or getXMLWait() functions.

Example of asynchronous GlideAjax call

Client Side:

var ga = new GlideAjax('HelloWorld');

ga.addParam('sysparm_name', 'helloWorld');

ga.addParam('sysparm_user_name', "Bob");

ga.getXML(HelloWorldParse);

function HelloWorldParse(response) {

  var answer = response.responseXML.documentElement.getAttribute("answer");

  alert(answer); }

Server Side Code:

var HelloWorld = Class.create();

HelloWorld.prototype = Object.extendsObject(AbstractAjaxProcessor, {

   helloWorld:function() { return "Hello " + this.getParameter('sysparm_user_name') + "!"; } ,

   _privateFunction: function() { // this function is not client callable     

    }

 });

Note: You must set the name of the script include to HelloWorld.

• ·         The sys_script_include code must extend the AbstractAjaxProcessorclass and be client-callable.
• ·         Function names starting with "_" are considered private and are not callable from the client.
• ·         Avoid overriding methods of AbstractAjaxProcessor, including initialize. While it is possible to invoke methods of your superclass object which you have overridden, it is complicated and best avoided altogether.