diff --git a/Libraries/LibJS/AST.cpp b/Libraries/LibJS/AST.cpp
index c612c3028cf..b9ee359d4a8 100644
--- a/Libraries/LibJS/AST.cpp
+++ b/Libraries/LibJS/AST.cpp
@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/StringBuilder.h>
 #include <LibJS/AST.h>
@@ -476,31 +477,42 @@ void Identifier::dump(int indent) const
 
 Value AssignmentExpression::execute(Interpreter& interpreter) const
 {
-    ASSERT(m_lhs->is_identifier());
-    auto name = static_cast<const Identifier&>(*m_lhs).string();
+    AK::Function<void(Value)> commit;
+    if (m_lhs->is_identifier()) {
+        commit = [&](Value value) {
+            auto name = static_cast<const Identifier&>(*m_lhs).string();
+            interpreter.set_variable(name, value);
+        };
+    } else if (m_lhs->is_member_expression()) {
+        commit = [&](Value value) {
+            auto object = static_cast<const MemberExpression&>(*m_lhs).object().execute(interpreter).to_object(interpreter.heap());
+            ASSERT(object.is_object());
+            auto property_name = static_cast<const Identifier&>(static_cast<const MemberExpression&>(*m_lhs).property()).string();
+            object.as_object()->put(property_name, value);
+        };
+    } else {
+        ASSERT_NOT_REACHED();
+    }
+
     auto rhs_result = m_rhs->execute(interpreter);
 
     switch (m_op) {
     case AssignmentOp::Assignment:
-        interpreter.set_variable(name, rhs_result);
         break;
     case AssignmentOp::AdditionAssignment:
         rhs_result = add(m_lhs->execute(interpreter), rhs_result);
-        interpreter.set_variable(name, rhs_result);
         break;
     case AssignmentOp::SubtractionAssignment:
         rhs_result = sub(m_lhs->execute(interpreter), rhs_result);
-        interpreter.set_variable(name, rhs_result);
         break;
     case AssignmentOp::MultiplicationAssignment:
         rhs_result = mul(m_lhs->execute(interpreter), rhs_result);
-        interpreter.set_variable(name, rhs_result);
         break;
     case AssignmentOp::DivisionAssignment:
         rhs_result = div(m_lhs->execute(interpreter), rhs_result);
-        interpreter.set_variable(name, rhs_result);
         break;
     }
+    commit(rhs_result);
     return rhs_result;
 }
 
diff --git a/Libraries/LibJS/AST.h b/Libraries/LibJS/AST.h
index 5fe383a3159..f4cc905285e 100644
--- a/Libraries/LibJS/AST.h
+++ b/Libraries/LibJS/AST.h
@@ -49,6 +49,7 @@ public:
     virtual Value execute(Interpreter&) const = 0;
     virtual void dump(int indent) const;
     virtual bool is_identifier() const { return false; }
+    virtual bool is_member_expression() const { return false; }
 
 protected:
     ASTNode() {}
@@ -124,8 +125,6 @@ private:
 };
 
 class Expression : public ASTNode {
-public:
-    virtual bool is_member_expression() const { return false; }
 };
 
 class FunctionNode {
@@ -594,6 +593,7 @@ public:
     virtual void dump(int indent) const override;
 
     const Expression& object() const { return *m_object; }
+    const Expression& property() const { return *m_property; }
 
 private:
     virtual bool is_member_expression() const override { return true; }
diff --git a/Libraries/LibJS/Runtime/Object.cpp b/Libraries/LibJS/Runtime/Object.cpp
index 2ddc4dfe174..d1211c2d396 100644
--- a/Libraries/LibJS/Runtime/Object.cpp
+++ b/Libraries/LibJS/Runtime/Object.cpp
@@ -60,6 +60,17 @@ Value Object::get(String property_name) const
 
 void Object::put(String property_name, Value value)
 {
+    Object* object = this;
+    while (object) {
+        auto value_here = object->m_properties.get(property_name);
+        if (value_here.has_value()) {
+            if (value_here.value().is_object() && value_here.value().as_object()->is_native_property()) {
+                static_cast<NativeProperty*>(value_here.value().as_object())->set(const_cast<Object*>(this), value);
+                return;
+            }
+        }
+        object = object->prototype();
+    }
     m_properties.set(property_name, move(value));
 }