5 files changed, 42 insertions, 2 deletions
diff --git a/Libraries/LibJS/AST.cpp b/Libraries/LibJS/AST.cpp
index c5e670fa7a..9a5ca84aaf 100644
--- a/Libraries/LibJS/AST.cpp
+++ b/Libraries/LibJS/AST.cpp
@@ -63,7 +63,18 @@ Value CallExpression::execute(Interpreter& interpreter) const
     for (size_t i = 0; i < m_arguments.size(); ++i)
         argument_values.append(m_arguments[i].execute(interpreter));
 
-    return function->call(interpreter, move(argument_values));
+    Value this_value = js_undefined();
+    if (m_callee->is_member_expression())
+        this_value = static_cast<const MemberExpression&>(*m_callee).object().execute(interpreter).to_object(interpreter.heap());
+
+    if (!this_value.is_undefined())
+        interpreter.push_this_value(this_value);
+
+    auto result = function->call(interpreter, move(argument_values));
+
+    if (!this_value.is_undefined())
+        interpreter.pop_this_value();
+    return result;
 }
 
 Value ReturnStatement::execute(Interpreter& interpreter) const
diff --git a/Libraries/LibJS/AST.h b/Libraries/LibJS/AST.h
index c5ded7710a..43a2508769 100644
--- a/Libraries/LibJS/AST.h
+++ b/Libraries/LibJS/AST.h
@@ -142,6 +142,7 @@ private:
 
 class Expression : public ASTNode {
 public:
+    virtual bool is_member_expression() const { return false; }
 };
 
 class ErrorExpression final : public Expression {
@@ -521,7 +522,10 @@ public:
     virtual Value execute(Interpreter&) const override;
     virtual void dump(int indent) const override;
 
+    const Expression& object() const { return *m_object; }
+
 private:
+    virtual bool is_member_expression() const override { return true; }
     virtual const char* class_name() const override { return "MemberExpression"; }
 
     NonnullOwnPtr<Expression> m_object;
diff --git a/Libraries/LibJS/Interpreter.h b/Libraries/LibJS/Interpreter.h
index 61b584c068..79940cac3a 100644
--- a/Libraries/LibJS/Interpreter.h
+++ b/Libraries/LibJS/Interpreter.h
@@ -79,10 +79,20 @@ public:
     void enter_scope(const ScopeNode&, Vector<Argument>, ScopeType);
     void exit_scope(const ScopeNode&);
 
+    void push_this_value(Value value) { m_this_stack.append(move(value)); }
+    void pop_this_value() { m_this_stack.take_last(); }
+    Value this_value() const
+    {
+        if (m_this_stack.is_empty())
+            return m_global_object;
+        return m_this_stack.last();
+    }
+
 private:
     Heap m_heap;
 
     Vector<ScopeFrame> m_scope_stack;
+    Vector<Value> m_this_stack;
 
     Object* m_global_object { nullptr };
 };
diff --git a/Libraries/LibJS/Object.cpp b/Libraries/LibJS/Object.cpp
index ae1d43397a..8fdd3721b2 100644
--- a/Libraries/LibJS/Object.cpp
+++ b/Libraries/LibJS/Object.cpp
@@ -42,7 +42,14 @@ Object::~Object()
 
 Value Object::get(String property_name) const
 {
-    return m_properties.get(property_name).value_or(js_undefined());
+    const Object* object = this;
+    while (object) {
+        auto value = object->m_properties.get(property_name);
+        if (value.has_value())
+            return value.value();
+        object = object->prototype();
+    }
+    return js_undefined();
 }
 
 void Object::put(String property_name, Value value)
@@ -58,6 +65,8 @@ void Object::put_native_function(String property_name, AK::Function<Value(Interp
 void Object::visit_children(Cell::Visitor& visitor)
 {
     Cell::visit_children(visitor);
+    if (m_prototype)
+        visitor.visit(m_prototype);
     for (auto& it : m_properties)
         visitor.visit(it.value);
 }
diff --git a/Libraries/LibJS/Object.h b/Libraries/LibJS/Object.h
index 30cc74bf6e..e3b8f1e4f9 100644
--- a/Libraries/LibJS/Object.h
+++ b/Libraries/LibJS/Object.h
@@ -45,12 +45,18 @@ public:
 
     virtual bool is_function() const { return false; }
     virtual bool is_native_function() const { return false; }
+    virtual bool is_string_object() const { return false; }
 
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_children(Cell::Visitor&) override;
 
+    Object* prototype() { return m_prototype; }
+    const Object* prototype() const { return m_prototype; }
+    void set_prototype(Object* prototype) { m_prototype = prototype; }
+
 private:
     HashMap<String, Value> m_properties;
+    Object* m_prototype { nullptr };
 };
 
 }