No, we don't have direct control over elements kinds, but we can write code that allows V8 to use the most efficient kind for the particular data set. Mathias Bynens described this and other performance tips in the corresponding V8 blog post:

In my opinion, it doesn't make a lot of sense to try to apply all of the tips to all of your code. But for performance-critical parts (the hop path) they're certainly valuable.

Software engineer at Hazelcast. Node.js core collaborator. Architectural design and challenging problems are the things that I love in IT.