Look at V8 De-Optimization List (--trace-opt)

[hostilefork]

From: "Writing Memory-Efficient JavaScript"

"Certain patterns will cause V8 to bail out of optimizations. A try-catch, for example, will cause such a bailout. For more information on what functions can and can’t be optimized, you can use --trace-opt file.js with the d8 shell utility that comes with V8."

In addition to whatever WASM profiling, looking at whatever this is could be good.

There's a fair number of other pointers in that article that are probably worth looking into, at some point--not for micro-optimization, but maybe just getting a feeling for what sorts of things are taking time.