Let me explain. From what I understand, V8 takes your JS and compiles it into machine language (not bytecode) with output being placed in the RAM instead of being written into a separate file on the drive. Optimizations follow as per future requirements.
And how does SpiderMonkey work? Seems it's quite like Chakra/ChakraCore.
While we are at it, would you kindly explain HHVM and php 7 in the same context? Is the bytecode JITed or is the source code JITed? Or is it both?