LibJS: Allow function calls with missing arguments

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.

1 files changed, 1 insertions, 1 deletions

diff --git a/Libraries/LibJS/Interpreter.h b/Libraries/LibJS/Interpreter.h
index fe806f9a4f..f65ae60386 100644
--- a/Libraries/LibJS/Interpreter.h
+++ b/Libraries/LibJS/Interpreter.h
@@ -79,7 +79,7 @@ public:
 
     void unwind(ScopeType type) { m_unwind_until = type; }
 
-    Value get_variable(const FlyString& name);
+    Optional<Value> get_variable(const FlyString& name);
     void set_variable(const FlyString& name, Value, bool first_assignment = false);
     void declare_variable(const FlyString& name, DeclarationType);