Ajax Request in Javascript

script.js

jQuery.ajax({
	url: dnStrings.ajax_url,
	data: {
		'since':wpNotifyCurrentDate
	},
	method: 'GET',
	beforeSend: function ( xhr ) {
			xhr.setRequestHeader( 'X-WP-Nonce', dnStrings.nonce );
	},
	success: function( response ){
		var msg_send = false;
		for( var i = 0; i < response.length; i++ ){
			if( -1 == jQuery.inArray( response[i].type + '-' +response[i].id, wpNotifiedIDs ) && !msg_send){
				msg_send = true;
				wpNotifiedIDs.push( response[i].type + '-' + response[i].id );
				window[dnStrings.callback]( response[i].title, response[i].content, response[i].avatar, response[i].link );
			}
		}
		if( response.length > 0 )
			sessionStorage.setItem( 'wpNotifiedIDs', wpNotifiedIDs );
		}
	}
);