App Part issues, spPageContextInfo - sharepoint-2013

Question

I am trying to create an SharePoint hosted app that contains an app part, this app part should show what the user is following. I have used working code as an example in the app, but I don't get it to work inside of the App Part.
I get this within the app part: "Uncaught ReferenceError: _spPageContextInfo is not defined".
If anyone has a real example how to make this work inside an app part, and using social.following, please help!
This is the code in App.js:
var headline = new Array("People", "Documents", "Sites");
var ActorImg = new Array("/_layouts/15/images/person.gif", "/_layouts/15/images/lg_ICGEN.gif", "/_layouts/15/images/siteicon_16x16.png");
function doJSON(RESTuri, success, fail) {
var restUrl = _spPageContextInfo.webAbsoluteUrl + RESTuri;
var executor = new SP.RequestExecutor(_spPageContextInfo.webAbsoluteUrl);
executor.executeAsync(
{
url: restUrl,
method: "GET",
headers: { "Accept": "application/json; odata=verbose" },
success: success,
error: fail
}
);
}
function renderSuccess(data) {
var jsonObject = JSON.parse(data.body);
var n = document.getElementById('jsonout');
n.innerHTML = data.body;
var results = jsonObject.d.Followed.results;
var str = '';
var old = -1;
var img = null;
for (j = 0; j < 5; j++) {
str += "<div class=\"container container" + j + "\">";
for (i = 0; i < results.length; i++) {
if (j != results[i].ActorType) continue;
if (old != results[i].ActorType) str += "<h1 class=\"headline" + results[i].ActorType + "\">" + headline[results[i].ActorType] + "</h1>";
img = results[i].ImageUri;
if (img == null) img = ActorImg[results[i].ActorType];
switch (results[i].ActorType) {
case 0:
// Use case: depending on ActorType if you want to use indiviual markup for every item-type
str += "<a title=\"" + results[i].Name + "\" class=\"link" + results[i].ActorType + "\" style=\"background-image:url(" + img + ")\" href=\"" + results[i].Uri + "\">" + results[i].Name + "</a>";
break;
default:
str += "<a title=\"" + results[i].Name + "\" class=\"link" + results[i].ActorType + "\" style=\"background-image:url(" + img + ")\" href=\"" + results[i].Uri + "\">" + results[i].Name + "</a>";
break;
}
old = results[i].ActorType;
}
str += "</div>";
}
n = document.getElementById('htmlout');
n.innerHTML = str + "<h1></h1>";
}
function renderFail(data, errorCode, errorMessage) {
n = document.getElementById('htmlout');
n.innerHTML = errorMessage;
}
$(document).ready(function () {
doJSON("/_api/social.following/my/followed%28types=15%29", renderSuccess, renderFail);
});
This is the div that's being used in both the app page(default.aspx) and the app part page(AppPart.aspx):
<div class="classic">
<pre id="jsonout" style="display: none;"></pre>
<div id="htmlout"></div>
</div>

Answer 1

Sorry guys. I solved it by just adding a reference to the sp.requestexecutor.js file, and parsed the host- and app-url from the querystring