Based on my test-nn which is based on the Step by Step Guide to Implementing a Neural Network in C by John A. Bullinaria.
Below are 4 runs testing Nodev8 and Nodev9 compiled for ES5 and ES6. What we see is that on Nodev8 ES5 is 6x times faster than ES6, 481,000 vs 75,000 eps.
For Nodev9 ES5 and ES6 run approximately the same speed 820,000 eps which is about 1.7x faster than Nodev8 using ES5!
$ node --version v8.1.2 $ node -e "console.log(process.versions.v8)" 5.8.283.41 $ ./nodev9/bin/node --version v9.0.0-v8-canary201706199cf43ea3fd $ ./nodev9/bin/node -e "console.log(process.versions.v8)" 6.1.0 (candidate) $ node build/test-nn.js 10000000 Epoch=10,000,000 Error=4.58e-8 time=20.76s eps=481,765 Pat Input0 Input1 Target0 Output0 0 0 0 0 0.00014153806736740904 1 1 0 1 0.9998568235021613 2 0 1 1 0.9998568475569924 3 1 1 0 0.0001748320545000856 $ node build/test-nn.js 10000000 Epoch=10,000,000 Error=4.58e-8 time=132.83s eps=75,284 Pat Input0 Input1 Target0 Output0 0 0 0 0 0.00014153806736740904 1 1 0 1 0.9998568235021613 2 0 1 1 0.9998568475569924 3 1 1 0 0.0001748320545000856 $ nodev9/bin/node build/test-nn.js 10000000 Epoch=10,000,000 Error=4.58e-8 time=12.10s eps=826,241 Pat Input0 Input1 Target0 Output0 0 0 0 0 0.00014153806736740904 1 1 0 1 0.9998568235021613 2 0 1 1 0.9998568475569924 3 1 1 0 0.0001748320545000856 $ nodev9/bin/node build/test-nn.js 10000000 Epoch=10,000,000 Error=4.58e-8 time=12.23s eps=817,394 Pat Input0 Input1 Target0 Output0 0 0 0 0 0.00014153806736740904 1 1 0 1 0.9998568235021613 2 0 1 1 0.9998568475569924 3 1 1 0 0.0001748320545000856