JIT Compilation flow
Parsing
(process) to read Source Code & generate AST.
Compilation
(process) to converts AST into Machine Code
Execution
(process) to run Machine Code immediately in Call Stack
Optimisation
(process) Optimization Compiler recompiles Code in background during Execution
Source: A crash course in just-in-time (JIT) compilers - Mozilla Hacks - the Web developer blog