Error in viewing files in Autodesk forge viewer - error calling doc.getRootItem() - autodesk-forge

Question

When viewing files in Autodesk forge viewer, getting the following errors,
Cannot read property ‘setEndpoint’ of undefined. Screenshot
doc.getRootItem is not a function. Screenshot
And will be able to view after empty cache and hard reload (Ctrl + Shift +R) the page. Sometimes the same errors will persist even after hard reload and clearing browser cache.
Code for the second error.
var options = {
env: 'AutodeskProduction',
accessToken: getAccessToken() //Method to get access token- no errors here
};
var documentId = 'urn:' + urn;
Autodesk.Viewing.Initializer(options, function onInitialized() {
Autodesk.Viewing.Document.load(documentId, onDocumentLoadSuccess, onDocumentLoadFailure);
});
//Autodesk.Viewing.Document.load - success function.
function onDocumentLoadSuccess(doc) {
setTimeout(function() {
debugger;
}, 5000);
//Error is thrown in the line below.
var viewables = Autodesk.Viewing.Document.getSubItemsWithProperties(doc.getRootItem(), {
'type': 'geometry'
}, true); //throws error on calling doc.getRootItem()
if (viewables.length === 0) {
console.error('Document contains no viewables.');
return;
}
// Choose any of the avialble viewables
var initialViewable = viewables[0];
var svfUrl = doc.getViewablePath(initialViewable);
var modelOptions = {
sharedPropertyDbPath: doc.getPropertyDbPath()
};
var viewerDiv = document.getElementById('divViewer');
viewer = new Autodesk.Viewing.Private.GuiViewer3D(viewerDiv);
viewer.start(svfUrl, modelOptions, onLoadModelSuccess, onLoadModelError);
}

Answer 1

You must have unwitting upgraded to Viewer V7 with which getRootItem and several other functions have been deprecated - see here for its release notes and migration guide.
Stick with V6 with <script src="https://developer-stg.api.autodesk.com/modelderivative/v2/viewers/viewer3D.js?v=6.6"></script> - if you don't specify a version by default the latest stable version would be served which is now V7.0.