If a JavaScript function is called more than six times, or loops more than 100 times, it gets fed into the next stage: a basic JIT compiler that produces executable code.

Both were introduced three years ago as a part of a two-tier compiler system. Ignition is a bytecode interpreter whose job is to start executing the JavaScript with as little delay as possible.

Tim Hart and Mike Levin at MIT created the first LISP compiler, in LISP, in 1962; the compiler itself was compiled by running Russell’s LISP interpreter on the compiler source code.