how to use the .impl methods in forge viewer V7* - autodesk-forge

Question

I have been using following .impl methods in V6*
viewerApp.getCurrentViewer().impl.invalidate
viewerApp.getCurrentViewer().impl.matman()._materials
How to proceed with V7*
Thank you
EDIT :
var options = {
env: 'AutodeskProduction',
api: 'derivativeV2',
getAccessToken: function(onTokenReady) {
var token = accessToken;
var timeInSeconds = 3600;
onTokenReady(token, timeInSeconds);
}
};
var documentId = "urn:" + urn;
Autodesk.Viewing.Initializer(options, function() {
var htmlDiv = document.getElementById('forgeViewer');
viewer = new Autodesk.Viewing.GuiViewer3D(htmlDiv);
var startedCode = viewer.start();
if (startedCode > 0) {
console.error('Failed to create a Viewer: WebGL not supported.');
return;
}
console.log('Initialization complete, loading a model next...');
Autodesk.Viewing.Document.load(documentId, onDocumentLoadSuccess, onDocumentLoadFailure);
});
...
Then I'm using impl methods as below ..
var mats = viewer.impl.matman()._materials;
But I still get the error
Cannot read property 'impl' of null
not sure why but may be my global viewer variable is null , any idea why this is happening or what have i done wrong.

Answer 1

Anything under the impl is typically considered internal implementation, and as such should not be relied on in production code. With that said, the impl property is still available, and if needed, you can use it in Forge Viewer version 7.* like so:
const viewer = new Autodesk.Viewing.GuiViewer3D(...);
viewer.impl.invalidate();
viewer.impl.matman();