index is a property and can be accessed directly

test/unit/geometry/EdgesGeometry.js

@@ -163,7 +163,7 @@ function createIndexedBufferGeometry ( vertList, idxList ) {
 
 function addDrawCalls ( geometry ) {
 
-	var numTris = geometry.getAttribute( 'index' ).count / 3;
+	var numTris = geometry.index.count / 3;
 
 	var offset = 0;
 	for ( var i = 0 ; i < numTris; i ++ ) {