I can't imagine writing an interpreter for JS that handles all its autoconversion foibles, and now with several more generations of ECMAScript version features

I can't imagine writing an interpreter for JS that handles all its autoconversion foibles, and now with several more generations of ECMAScript version features piled on (generally for the better), that's a lot more to handle. And then have to do all the type inferencing to try to get performance, and then the dynamic compiling...