SharePoint Hosted App Office 365 : could not complete cross domain call

Question

I am trying to create one SharePoint hosted App on office 365.

I am trying to access the list item from host web, but it goes to error every time.

Please suggest me if i am missing something.

Please refer the following code i have written.

var hostweburl;
var appweburl;

$(document).ready(function () {

    hostweburl = decodeURIComponent(getQueryStringParameter("SPHostUrl"));
    appweburl = decodeURIComponent(getQueryStringParameter("SPAppWebUrl"));

    var scriptbase = hostweburl + "/_layouts/15/";
    $.getScript(scriptbase + "SP.RequestExecutor.js", runCrossDomainRequest);

});

function runCrossDomainRequest() {
    var executor = new SP.RequestExecutor(hostweburl);
    executor.executeAsync(
        {
            url: hostweburl +"/_api/web/lists/getbytitle('Announcements')/items",
            method: "GET",
            headers: {
                "Accept": "application/json; odata=verbose",
                //"content-type": "application/json;odata=verbose",
                //"X-RequestDigest": $("#__REQUESTDIGEST").val()
            },
            success: successHandler,
            error: errorHandler
        }
    );
}

function successHandler(data) {
    alert("In Success");
    var jsonObject = JSON.parse(data.body);

}

function errorHandler(data, errorCode, errorMessage) {
    alert("could not complete cxoss domain call : " + errorMessage);
}
function getQueryStringParameter(paramToRetrieve) {
    var params =
        document.URL.split("?")[1].split("&");
    var strParams = "";
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == paramToRetrieve)
            return singleParam[1];
    }
}

Answer 1

I reviewed the code that looks like the mentioned at MSDN article Access SharePoint 2013 data from add-ins using the cross-domain library That should be working !!

So I think the issue is related to the APP permission, where you need to set the Site collection Scope to Read Permission as the following

• In Solution Explorer > Double click on AppManifest to open it.
• Click on the Permissions tab > At the Scope Column > Set Site collection to Read at Permission Column.

[Update]

Regarding SharePoint App Web URL vs SharePoint Host Web URL

• SharePoint App Web URL is the site URL that the APP will be deployed.
• SharePoint Host Web URL is the site URL that the APP will be installed.