How do native Javascript functions work in V8?

Question

I am trying to figure out how some Javascript native functions and operators (shorthand functions) are implemented under the hood in Chrome's V8. In particular, I'm trying to understand how the Unary (-) operation works.

I have found the code for unary operators in V8 here

Could someone explain what's happening here:

Type* Typer::Visitor::JSTypeOfTyper(Type* type, Typer* t) {
  Factory* const f = t->isolate()->factory();
  if (type->Is(Type::Boolean())) {
    return Type::Constant(f->boolean_string(), t->zone());
  } else if (type->Is(Type::Number())) {
    return Type::Constant(f->number_string(), t->zone());
  } else if (type->Is(Type::String())) {
    return Type::Constant(f->string_string(), t->zone());
  } else if (type->Is(Type::Symbol())) {
    return Type::Constant(f->symbol_string(), t->zone());
  } else if (type->Is(Type::Union(Type::Undefined(), Type::OtherUndetectable(),
                                  t->zone()))) {
    return Type::Constant(f->undefined_string(), t->zone());
  } else if (type->Is(Type::Null())) {
    return Type::Constant(f->object_string(), t->zone());
  } else if (type->Is(Type::Function())) {
    return Type::Constant(f->function_string(), t->zone());
  } else if (type->IsConstant()) {
    return Type::Constant(
        Object::TypeOf(t->isolate(), type->AsConstant()->Value()), t->zone());
  }
  return Type::InternalizedString();
}


Type* Typer::Visitor::TypeJSTypeOf(Node* node) {
  return TypeUnaryOp(node, JSTypeOfTyper);
}

I have absolutely no background on C++, as I'm a web developer, so I can't seem to understand what's happening. Thanks!

I guess what without goog knowledge of v8 architecture no one could explain what's happening here. Why exactly do you want to dig so deep? — Denis Sheremet
– Denis Sheremet, Commented Oct 4, 2016 at 10:27
The problem here that this question cannot be answered without deep knowledge of the v8 implementation. It is clear that the code identifies the type of type and takes a corresponding representation of it. For more explanation maybe contact a developer, or study the documentation v8docs.nodesource.com — plasmacel
– plasmacel, Commented Oct 4, 2016 at 11:42

user835611 · Accepted Answer · 2016-10-04 16:07:32Z

2

I think - is turned into multiplication by -1.

src/parsing/parser.cc

  // The same idea for '-foo' => 'foo*(-1)'.
  if (op == Token::SUB) {
    return factory()->NewBinaryOperation(
         Token::MUL, expression, factory()->NewNumberLiteral(-1, pos), pos);
  }

Do you want to say in more detail what you want to understand about -?

answered Oct 4, 2016 at 16:07

user835611

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2 Comments

nikjohn Over a year ago

That looks like what I was looking for. Could you link me to the LOC?

user835611 Over a year ago

It's in src/parsing/parser.cc line 466.

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