How to call GlideAjax in client script and return data in JSON ServiceNow

Client Script
var ga = new GlideAjax('MyCustomAjax');
ga.addParam('sysparm_name', 'helloWorld');
ga.addParam('sysparm_hoge', g_form.getValue("email")); // When you want to pass a value
ga.getXMLAnswer(callback);
 function callback(answer){
  var getanswer = answer.evalJSON();
    g_form.addInfoMessage(getanswer.var1); //Display "Hello"
    g_form.addInfoMessage(getanswer.var2);
}
  Script Include
var MyCustomAjax = Class.create();
MyCustomAjax.prototype = Object.extendsObject(AbstractAjaxProcessor, {
     helloWorld: function() {
        var obj = {};
         obj.var1 = 'Hello';
        obj.var2 = 'World';
         var json = new JSON();
        var data = json.encode(obj);//JSON formatted string
         return data;
    },
     type: 'MyCustomAjax'
});