ThreeJS, Ionic, Angular2+ - How to modify position BufferGeometry / BufferAttribute values - It says Index Signature ArrayLike<number> is read only

Question

I have everything for a 3d implementation with Three.js working in a plain js app. I am using BufferGeometry for lines and meshes and I am modifying the position attribute to modify their shapes.

Now I am using Ionic and converting the 3d stuff to be inside an angular component. I have everything working except I am unable to update the position values in the bufferAttribute.

I was using this in the original js to get positions array to modify:

var vrts = myMesh.geometry.attributes.position.array;

Then I could modify and set the vrts array values with things like:

vrts[0] = newValue;

and I was then setting needsUpdate = true with:

myMesh.geometry.attributes.position.needsUpdate = true;

Everything was working fine in the js app.

In the Ionic app, when I tried to point to get positions array it said: Property 'attributes' does not exist on type BufferGeometry | Geometry so I converted to this:

vrts = (this.geometry.getAttribute("position"));

and now I can access the values with:

vertexValue = vrts.array[0];

But, when I try to modify the value, ie:

vrts.array[0] = newValue;

It says: error TS2542: Index signature in type 'ArrayLike< number>' only permits reading

and won't allow me to modify the value.

I also had some trouble accessing the needsUpdate variable. I was previously using:

myMesh.geometry.attributes.position.needsUpdate = true;

and have now converted to this, but not sure if it is correct:

(<THREE.BufferAttribute>vrts).needsUpdate = true;

I am also trying to set the 'positions' array to be dynamic with the following statement:

(<THREE.BufferAttribute>this._geometry.getAttribute("position")).setUsage(THREE.DynamicDrawUsage);

I am using BufferGeometry for lines and meshes. Maybe my alternative is to create a new positions array and use setAttribute('position', newPositions) each time I modify things, but it seems like this would defeat the purpose of efficient memory use by allocating new memory every time things are changed.

Thank you for your advice!