Fetch SharePoint List Item in SharePoint Hosted APP

This Peace of code fetches the data from the SharePoint list which is written in SharePoint hosted app.

App.JS

'use strict';
var listItems;
var hostweburl = decodeURIComponent(getQueryStringParameter('SPHostUrl'));
var appweburl = decodeURIComponent(getQueryStringParameter('SPAppWebUrl'));
$(document).ready(function()
{
    SP.SOD.executeFunc('sp.js', 'SP.ClientContext', GetListItems)
});

function GetListItems()
{
    var context = new SP.ClientContext(appweburl);
    var appContextSite = new SP.AppContextSite(_context, hostweburl);
    var web = appContextSite.get_web();
    context.load(web);
    var list = web.get_lists().getByTitle("Test");
    var camlQuery = SP.CamlQuery.createAllItemsQuery();
    listItems = list.getItems(camlQuery);
    context.load(listItems);
    context.executeQueryAsync(Function.createDelegate(this, function()
    {
        var ListEnumerator = listItems.getEnumerator();
        var listItemTitleAndId = '';
        while(ListEnumerator.moveNext())
        {
            var iTemFromTestList = ListEnumerator.get_current();
            listItemTitleAndId += "Id " + iTemFromTestList.get_item('ID') + " Title " + iTemFromTestList.get_item('Title')
        }
        alert(listItemTitleAndId);
        console.log(listItemTitleAndId);
    }), Function.createDelegate(this, function(sender, args)
    {
        alert("Fail")
        console.log("Error : " + args.get_stackTrace());
    }));
}

function getQueryStringParameter(paramToRetrieve)
{
    var params = document.URL.split("?")[1].split("&");
    for(var i = 0; i < params.length; i = i + 1)
    {
        var singleParam = params[i].split("=");
        if(singleParam[0] == paramToRetrieve) return singleParam[1];
    }
}