This might be entirely possible with streams. In any case, I couldn’t figure complete stream solution out. But this solutions subscribes to the stream and tweens the value without directly accessing the DOM.
In any case, generally when dealing with animations - I actually think direct DOM manipulation is the best for performance. But since the animations here don’t involve hundreds of “steps”, the perf cost is negligible for this example.
Edit: here is the same solution as a helper and a stream JS Bin - Collaborative JavaScript Debugging
Edit 2: you could take it a step further and use them as subexpressions to animate declaratively JS Bin - Collaborative JavaScript Debugging