gef | GDB Enhanced Features ) - a modern experience | Hacking library

(V8 developer here.)

Many things in V8 have more than one implementation, for various reasons: in this case, there's the C++ way of adding an entry to an OrderedHashMap (which you've found), and there's also a generated-code way of doing it. If you grep for MapPrototypeSet, you'll find TF_BUILTIN(MapPrototypeSet, ... in builtins-collections-gen.cc, which is the canonical implementation of Map.prototype.set. Since that's a piece of code that runs at V8 build time to generate a "stub" which is then embedded into the binary, there's no direct way of setting a breakpoint into that stub. One way to do it is to insert a DebugBreak() call into the stub-generating code, and recompile.

Not all builtins are implemented in the same way:

• some (like M.p.set) are generated "CSA builtins" in src/builtins/*-gen.cc
• some are regular C++ in src/builtins/*.cc
• some are written in Torque (src/builtins/*.tq) which is V8's own DSL that translates to CSA
• some have fast paths directly in the compiler(s)
• some have their meat in "runtime functions" (src/runtime/*.cc)

Many have more than one implementation (typically a fully spec-compliant "slow" fallback, often but not always in C++, and then one or more fast paths that take shortcuts for common situations, often but not always in various forms of generated code). There are probably also a few special cases I'm forgetting right now; and as this post ages over the years, the enumeration above will become outdated (e.g. there used to be builtins in handwritten assembly, but we got rid of (almost all) of them; there used to be builtins generated by the old Crankshaft compiler, but we replaced that; there used to be builtins written in JavaScript, but we got rid of them; CSA was new at some point; Torque was new at some point; who knows what'll come next).

One consequence of all this is that questions like "how exactly does JavaScript's feature X work under the hood?" often don't have a concise answer.

Have fun with your investigation!

List.ForEach is not LINQ though

I figured it out.. just had to it with numpy

How about something like this:

You were almost there. The problem was in the place where you divide cnt = len(parsedlist/2).

Corrected code:

Here's a very basic implementation, using vanilla js.

Try with np.where:

You already was iterating over FrictionNumber with i, so you could just directly use the value i for comparing.

Here's one way, though I am sure it could be refined