How to view the assembly code generated from my JavaScript (in Chrome)?

Question

Is it possible to view the machine code (x86 instructions) that a browser ultimately generates from my JavaScript? E.g.

--- Raw source ---
function add(a, b){
  return a + b;
}
...

--- Code ---
source_position = 0
kind = FUNCTION
Instructions (size = 456)
0x36953100     0  8b4c2404       mov ecx,[esp+0x4]
0x36953104     4  81f991806049   cmp ecx,0x49608091          ;; object: 0x49608091 <undefined>
0x3695310a    10  750a           jnz 22  (0x36953116)
0x3695310c    12  8b4e13         mov ecx,[esi+0x13]
0x3695310f    15  8b4917         mov ecx,[ecx+0x17]
0x36953112    18  894c2404       mov [esp+0x4],ecx
0x36953116    22  55             push ebp

Answer 1

Your script isn't transformed to machine code directly. Chrome and Node.js run JavaScript on a virtual machine called V8 and you can get the VM bytecode using:

node --print-bytecode script.js

Then V8 executes and optimizes the bytecode and calls external C libraries and OS API (system calls) or Web API. Final machine code may vary even with the same JavaScript code (for example before and after optimization).

You can also start Chrome from the command line with --js-flags="--print-bytecode"

UPD:

As @PeterCordes noticed Node.js allows seeing the Turbofan generated machine code using

node --print-opt-code script.js

Chrome:

--js-flags="--print-opt-code"

Also you can use an HTML visualizer like https://github.com/v8/v8/tree/main/tools/turbolizer