getQueryStringParameter is not defined

Question

I have a SharePoint hosted app and I am trying to pull the SPHostUrl out of the app Url for REST calls.

Everything I read tells me to use the below but for some reason I am getting an error

'GetQueryStringParameter' is undefined

I have tried in a couple of different browsers and even tried just a simple command in the console using the browser developer tools but it seems GetQueryStringParameter() is not a valid function? am I missing something?

URL

http://app-cb941ae4f1f18e.app.dragon.dev/sites/smrgol/AppPartTest/Pages/Default.aspx?SPHostUrl=http%3A%2F%2Flair%2Edragon%2Edev%2Fsites%2Fsmrgol&SPLanguage=en%2DUS&SPClientTag=2&SPProductNumber=15%2E0%2E4763%2E1000&SPAppWebUrl=http%3A%2F%2Fapp%2Dcb941ae4f1f18e%2Eapp%2Edragon%2Edev%2Fsites%2Fsmrgol%2FAppPartTest

References in Default.aspx

<script type="text/javascript" src="../Scripts/jquery-1.9.1.min.js"></script>
<script type="text/javascript" src="/_layouts/15/MicrosoftAjax.js"></script>
<script type="text/javascript" src="/_layouts/15/sp.runtime.js"></script>
<script type="text/javascript" src="/_layouts/15/sp.js"></script>
<script type="text/javascript" src="../Scripts/App.js"></script>

Line in App.js

var hostUrl = decodeURIComponent(getQueryStringParameter("SPHostUrl"));

Answer 1

Definition of getQueryStringParameter should look like following. Check it in your App.js file.

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];
}

It is not needed actually, you can get by following way.

var spHostUrl = GetUrlKeyValue('SPHostUrl');

See following post for more explanation by Danny Engelman

https://sharepoint.stackexchange.com/a/159290/21421