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.
Added the ability to include a u8 attributes parameter with all of the
various put methods in the Object class. They can be omitted, in which
case it defaults to "Writable | Enumerable | Configurable", just like
before this commit.
All of the attribute values for each property were gathered from
SpiderMonkey in the Firefox console. Some properties (e.g. all of the
canvas element properties) have undefined property descriptors... not
quite sure what that means. Those were left as the default specified
above.
Everyone who constructs an Object must now pass a prototype object when
applicable. There's still a fair amount of code that passes something
fetched from the Interpreter, but this brings us closer to being able
to detach prototypes from Interpreter eventually.
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.)
