LibJS: Implement support for the [[IsHTMLDDA]] internal slot

Best regards from Annex B and document.all :^)

2 files changed, 15 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Object.h b/Userland/Libraries/LibJS/Runtime/Object.h
index 215ae7d4d3..cfdfb9b8d0 100644
--- a/Userland/Libraries/LibJS/Runtime/Object.h
+++ b/Userland/Libraries/LibJS/Runtime/Object.h
@@ -110,6 +110,9 @@ public:
     virtual bool is_native_function() const { return false; }
     virtual bool is_lexical_environment() const { return false; }
 
+    // B.3.7 The [[IsHTMLDDA]] Internal Slot, https://tc39.es/ecma262/#sec-IsHTMLDDA-internal-slot
+    virtual bool is_htmldda() const { return false; }
+
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_edges(Cell::Visitor&) override;
 
diff --git a/Userland/Libraries/LibJS/Runtime/Value.cpp b/Userland/Libraries/LibJS/Runtime/Value.cpp
index 1f3de02866..8461966fac 100644
--- a/Userland/Libraries/LibJS/Runtime/Value.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Value.cpp
@@ -275,6 +275,9 @@ String Value::typeof() const
     case Value::Type::String:
         return "string";
     case Value::Type::Object:
+        // B.3.7.3 Changes to the typeof Operator, https://tc39.es/ecma262/#sec-IsHTMLDDA-internal-slot-typeof
+        if (as_object().is_htmldda())
+            return "undefined";
         if (is_function())
             return "function";
         return "object";
@@ -383,6 +386,9 @@ bool Value::to_boolean() const
     case Type::BigInt:
         return m_value.as_bigint->big_integer() != BIGINT_ZERO;
     case Type::Object:
+        // B.3.7.1 Changes to ToBoolean, https://tc39.es/ecma262/#sec-IsHTMLDDA-internal-slot-to-boolean
+        if (m_value.as_object->is_htmldda())
+            return false;
         return true;
     default:
         VERIFY_NOT_REACHED();
@@ -1329,6 +1335,12 @@ bool abstract_eq(GlobalObject& global_object, Value lhs, Value rhs)
     if (lhs.is_nullish() && rhs.is_nullish())
         return true;
 
+    // B.3.7.2 Changes to IsLooselyEqual, https://tc39.es/ecma262/#sec-IsHTMLDDA-internal-slot-aec
+    if (lhs.is_object() && lhs.as_object().is_htmldda() && rhs.is_nullish())
+        return true;
+    if (lhs.is_nullish() && rhs.is_object() && rhs.as_object().is_htmldda())
+        return true;
+
     if (lhs.is_number() && rhs.is_string())
         return abstract_eq(global_object, lhs, rhs.to_number(global_object));