So I ran your two programs through SpiderNode just to see how they perform with SpiderMonkey as the engine instead of V8. As expected, the average time is a little higher, but that is especially true of the closure implementation. Running ten trials of both programs and taking the averages, I find that the class implementation takes about 11.65 seconds with an average resident set size of 40,099,430.4 bytes, a heap total of 9,437,184 bytes, a heap used of 6,022,144 bytes. The closure implementation takes 12.76 seconds with rss of 55,508,172.8 bytes, heap total of 16,777,216 bytes, and a heap used of12,836,696 bytes.

In other words, the time and memory differences are much smaller (both are inefficient when using SpiderNode), but the closure technique actually takes longer than the class implementation.

Good analysis. Interestingly, when I try to duplicate your results, the class implementation takes twice as long as the closure implementation (10 seconds vs 5). I'm using v4.2.6 of node, though. Clearly v6 makes a big difference.