How to implement ajax in magento? (frontend side)

ajax.phtml
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    Click To display records

app/code/local/companyname/helloworld/controllers/indexController.php
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class Companyname_HelloWorld_IndexController extends Mage_Core_Controller_Front_Action
  {  
    public function AjaxAction()  
      {  
       $this->loadLayout();  
       $this->renderLayout();  
      }
  }

app/design/frontend/default/themename/layout/helloworld.xml
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app/design/frontend/default/themename/template/page/ajax.phtml
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getChildHtml('content'); ?>

app/design/frontend/default/themename/template/helloworld/ajaxresponse.phtml
--------------------------------
echo "response of ajax is executed";
?>