Javscript is nowdays a mix of interpreter and compiled lannguage , it's called JIT compilation and let me tell you what's this and how our JS engine executes code.

so when you write the code , js engine tokenizes the code and converts it to AST ( a tree like structure ) then it goes to Profiler ,Profiler's main work is that check for the code that runs repetitively like a loop or a function which is called many times and it takes that part of the code and throw it to TurboFan Compiler , turbofan's main job is that it optimize and compiled that portion of code into optimized binary and then run. and other parts of code runs interpreted by Ignition compiler which converts the code into ByteCode and runs.