Reading this experience report from the DARPA challenge via Slashdot, I wondered: if event registration caused object retention, how can we deal with these memory issues in Flapjax?

Worrying about memory leaks in JavaScript is a losing battle — the browsers have different collectors. But given functional reactive programming in other settings (e.g., Java/C#), how can we solve this kind of problem? We looked at deletion briefly, but never had time to address the issue in detail. The complexity in our case is that the event registration encodes the entire application — how do you decide that a certain code path is dead? It may be helpful to view a functional-reactive program as a super-graph of data producing, splitting, merging, and consuming nodes; the application state is the subgraph induced by the active nodes reaching the consumers. Then there’s a certain static overhead for the program, plus the dynamic overhead of its active components.

Most of the Flapjax code I’ve written has been for the user interface, so binding and unbinding isn’t much of an issue: if the interface changes temporarily (e.g., tabs), the older behavior is usually recoverable and shouldn’t be collected. When working with more complex models with longer lived state, a deletion policy is more important. Shriram has been working on larger Flapjax applications with application logic as well as presentation — I wonder if he’s run into serious GC issues.