This commit introduces a way to get an object's own properties in the
correct order. The "correct order" for JS object properties is first all
array-like index properties (numeric keys) sorted by insertion order,
followed by all string properties sorted by insertion order.
Objects also now print correctly in the repl! Before this commit:
courage ~/js-tests $ js
> ({ foo: 1, bar: 2, baz: 3 })
{ bar: 2, foo: 1, baz: 3 }
After:
courage ~/js-tests $ js
> ({ foo: 1, bar: 2, baz: 3 })
{ foo: 1, bar: 2, baz: 3 }
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.
Normally the storage would be expanded by set_shape() upon transition
to a new shape, but if the shape is already unique, there is no new
transition so we have to expand the storage manually.
It turns out "delete" is actually a unary op :)
This patch implements deletion of object properties, it doesn't yet
work for casually deleting properties from the global object.
When deleting a property from an object, we switch that object to
having a unique shape, no longer sharing shapes with others.
Once an object has a unique shape, it no longer needs to care about
shape transitions.
JS::Value already has the empty state ({} or Value() gives you one.)
Use this instead of wrapping Value in Optional in some places.
I've also added Value::value_or(Value) so you can easily provide a
fallback value when one is not present.
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.
Object.defineProperty() can now change the attributes of a property
already on the object. Internally this becomes a shape transition with
the TransitionType::Configure. Such transitions don't expand the
property storage capacity, but rather simply keep attributes up to date
when generating a property table.
We now care (a little bit) about the "configurable" and "writable"
property attributes.
Property attributes are stored together with the property name in
the Shape object. Forward transitions are not attribute-savvy and will
cause poor Shape reuse in the case of multiple same-name properties
with different attributes.
Oh, and this patch also adds Object.getOwnPropertyDescriptor() :^)
This patch adds a new kind of JS::Value, the empty value.
It's what you get when you do JSValue() (or most commonly, {} in C++.)
An empty Value signifies the absence of a value, and should never be
visible to JavaScript itself. As of right now, it's used for array
holes and as a return value when an exception has been thrown and we
just want to unwind.
This patch is a bit of a mess as I had to fix a whole bunch of code
that was relying on JSValue() being undefined, etc.
Now that we have two separate storages for Object properties depending
on what kind of index they have, it's nice to have an abstraction that
still allows us to say "here's a property name".
We use PropertyName to always choose the optimal storage path directly
while interpreting the AST. :^)
Objects can have both named and indexed properties. Previously we kept
all property names as strings. This patch separates named and indexed
properties and splits them between Object::m_storage and m_elements.
This allows us to do much faster array-style access using numeric
indices. It also makes the Array class much less special, since all
Objects now have number-indexed storage. :^)
This patch adds JS::Shape, which implements a transition tree for our
Object class. Object property keys, prototypes and attributes are now
stored in a Shape, and each Object has a Shape.
When adding a property to an Object, we make a transition from the old
Shape to a new Shape. If we've made the same exact transition in the
past (with another Object), we reuse the same transition and both
objects may now share a Shape.
This will become the foundation of inline caching and other engine
optimizations in the future. :^)
Let's move towards using references over pointers in LibJS as well.
I had originally steered away from it because that's how I've seen
things done in other engines. But this is not the other engines. :^)
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.
Fix the "instanceof" operator to check if the constructor's prototype
property occurs anywhere in the prototype chain of the instance object.
This patch also adds Object.setPrototypeOf() to make it possible to
create a test for this bug.
Thanks to DexesTTP for pointing this out! :^)
We were interpreting "undefined" as a variable lookup failure in some
cases and throwing a ReferenceError exception instead of treating it
as the valid value "undefined".
This patch wraps the result of variable lookup in Optional<>, which
allows us to only throw ReferenceError when lookup actually fails.
Object now has virtual get_own_property() and put_own_property() member
functions that can be overridden to provide custom behavior.
We use these virtuals to move Array-specific access behavior to Array.
I'm not completely thrilled about Object::get() and Object::put() doing
special-case stuff for arrays, and we should probably come up with a
better abstraction for it.
But at least it works for now, which is really nice. :^)
This is pretty naive, we just walk up the prototype chain and call any
NativeProperty setter that we find. If we don't find one, we put/set
the value as an own property of the object itself.
