To allow implementing the DOM class hierarchy in JS bindings, this
patch adds an inherits() function that can be used to ask an Object
if it inherits from a specific C++ class (by name).
The necessary overrides are baked into each Object subclass by the
new JS_OBJECT macro, which works similarly to C_OBJECT in LibCore.
Thanks to @Dexesttp for suggesting this approach. :^)
More work towards supporting multiple global objects. Native C++ code
now get a GlobalObject& and don't have to ask the Interpreter for it.
I've added macros for declaring and defining native callbacks since
this was pretty tedious and this makes it easier next time we want to
change any of these signatures.
"[Function.length is] the number of formal parameters. This number
excludes the rest parameter and only includes parameters before
the first one with a default value." - MDN
Adds the ability for function arguments to have default values. This
works for standard functions as well as arrow functions. Default values
are not printed in a <function>.toString() call, as nodes cannot print
their source string representation.
This patch replaces the old variable lookup logic with a new one based
on lexical environments.
This brings us closer to the way JavaScript is actually specced, and
also gives us some basic support for closures.
The interpreter's call stack frames now have a pointer to the lexical
environment for that frame. Each lexical environment can have a chain
of parent environments.
Before calling a Function, we first ask it to create_environment().
This gives us a new LexicalEnvironment for that function, which has the
function's lexical parent's environment as its parent. This allows
inner functions to access variables in their outer function:
function foo() { <-- LexicalEnvironment A
var x = 1;
function() { <-- LexicalEnvironment B (parent: A)
console.log(x);
}
}
If we return the result of a function expression from a function, that
new function object will keep a reference to its parent environment,
which is how we get closures. :^)
I'm pretty sure I didn't get everything right here, but it's a pretty
good start. This is quite a bit slower than before, but also correcter!
We were allowing this dangerous kind of thing:
RefPtr<Base> base;
RefPtr<Derived> derived = base;
This patch changes the {Nonnull,}RefPtr constructors so this is no
longer possible.
To downcast one of these pointers, there is now static_ptr_cast<T>:
RefPtr<Derived> derived = static_ptr_cast<Derived>(base);
Fixing this exposed a ton of cowboy-downcasts in various places,
which we're now forced to fix. :^)
This adds Function::construct() for constructor function calls via `new`
keyword. NativeFunction doesn't have constructor behaviour by default,
ScriptFunction simply calls call() in construct()
Native functions now only get the Interpreter& as an argument. They can
then extract |this| along with any indexed arguments it wants from it.
This forces functions that want |this| to actually deal with calling
interpreter.this_value().to_object(), and dealing with the possibility
of a non-object |this|.
This is still not great but let's keep massaging it forward.
Now that Interpreter keeps all arguments in the CallFrame stack, we can
just pass a const-reference to the CallFrame's argument vector to each
function handler (instead of copying it.)
