diff --git a/js/src/frontend/BytecodeCompiler.cpp b/js/src/frontend/BytecodeCompiler.cpp
index 67423eb7ab..7f5b705f92 100644
--- a/js/src/frontend/BytecodeCompiler.cpp
+++ b/js/src/frontend/BytecodeCompiler.cpp
@@ -676,8 +676,13 @@ frontend::CompileLazyFunction(JSContext* cx, Handle<LazyScript*> lazy, const cha
     if (lazy->hasBeenCloned())
         script->setHasBeenCloned();
 
+    FieldInitializers fieldInitializers = FieldInitializers::Invalid();
+    if (fun->kind() == JSFunction::FunctionKind::ClassConstructor) {
+        fieldInitializers = lazy->getFieldInitializers();
+    }
+
     BytecodeEmitter bce(/* parent = */ nullptr, &parser, pn->as<FunctionNode>().funbox(), script, lazy,
-                        pn->pn_pos, BytecodeEmitter::LazyFunction);
+                        pn->pn_pos, BytecodeEmitter::LazyFunction, fieldInitializers);
     if (!bce.init())
         return false;
 
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index 72ba7c6ed0..02400ce2a3 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -156,7 +156,8 @@ class MOZ_RAII OptionalEmitter
 BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
                                  Parser<FullParseHandler>* parser, SharedContext* sc,
                                  HandleScript script, Handle<LazyScript*> lazyScript,
-                                 uint32_t lineNum, EmitterMode emitterMode)
+                                 uint32_t lineNum, EmitterMode emitterMode,
+                                 FieldInitializers fieldInitializers /* = FieldInitializers::Invalid() */)
   : sc(sc),
     cx(sc->context),
     parent(parent),
@@ -166,6 +167,7 @@ BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
     main(cx, lineNum),
     current(&main),
     parser(parser),
+    fieldInitializers_(fieldInitializers),
     atomIndices(cx->frontendCollectionPool()),
     firstLine(lineNum),
     maxFixedSlots(0),
@@ -178,10 +180,6 @@ BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
     innermostNestableControl(nullptr),
     innermostEmitterScope_(nullptr),
     innermostTDZCheckCache(nullptr),
-    fieldInitializers_(parent
-                       ? parent->fieldInitializers_
-                       : lazyScript ? lazyScript->getFieldInitializers()
-                                    : FieldInitializers::Invalid()),
 #ifdef DEBUG
     unstableEmitterScope(false),
 #endif
@@ -202,10 +200,11 @@ BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
 BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
                                  Parser<FullParseHandler>* parser, SharedContext* sc,
                                  HandleScript script, Handle<LazyScript*> lazyScript,
-                                 TokenPos bodyPosition, EmitterMode emitterMode)
+                                 TokenPos bodyPosition, EmitterMode emitterMode,
+                                 FieldInitializers fieldInitializers)
     : BytecodeEmitter(parent, parser, sc, script, lazyScript,
                       parser->tokenStream.srcCoords.lineNum(bodyPosition.begin),
-                      emitterMode)
+                      emitterMode, fieldInitializers)
 {
     setScriptStartOffsetIfUnset(bodyPosition.begin);
     setFunctionBodyEndPos(bodyPosition.end);
@@ -2321,6 +2320,10 @@ BytecodeEmitter::emitSetThis(BinaryNode* setThisNode)
         return false;
     }
 
+    if (!emitInitializeInstanceFields(true)) {
+        return false;
+    }
+
     return true;
 }
 
@@ -2399,6 +2402,9 @@ BytecodeEmitter::emitFunctionScript(FunctionNode* funNode)
     ListNode* paramsBody = &funNode->body()->as<ListNode>();
     FunctionBox* funbox = sc->asFunctionBox();
 
+    MOZ_ASSERT(fieldInitializers_.valid == (funbox->function()->kind() ==
+                                            JSFunction::FunctionKind::ClassConstructor));
+
     setScriptStartOffsetIfUnset(paramsBody->pn_pos.begin);
 
     //                [stack]
@@ -2433,6 +2439,8 @@ BytecodeEmitter::emitFunctionScript(FunctionNode* funNode)
     if (!fse.initScript())
         return false;
 
+    script->setFieldInitializers(fieldInitializers_);
+
     return true;
 }
 
@@ -5593,11 +5601,14 @@ BytecodeEmitter::emitComprehensionFor(ForNode* forNode)
 }
 
 MOZ_NEVER_INLINE bool
-BytecodeEmitter::emitFunction(FunctionNode* funNode, bool needsProto)
+BytecodeEmitter::emitFunction(FunctionNode* funNode, bool needsProto /* = false */,
+                              ListNode* classContentsIfConstructor /* = nullptr */)
 {
     FunctionBox* funbox = funNode->funbox();
     RootedFunction fun(cx, funbox->function());
-    
+
+    MOZ_ASSERT((classContentsIfConstructor != nullptr) == (funbox->function()->kind() ==
+                                                           JSFunction::FunctionKind::ClassConstructor));
     //                [stack]
 
     FunctionEmitter fe(this, funbox, funNode->syntaxKind(),
@@ -5627,6 +5638,9 @@ BytecodeEmitter::emitFunction(FunctionNode* funNode, bool needsProto)
                 return false;
             }
 
+            if (classContentsIfConstructor) {
+                fun->lazyScript()->setFieldInitializers(setupFieldInitializers(classContentsIfConstructor));
+            }
             return true;
         }
 
@@ -5651,8 +5665,13 @@ BytecodeEmitter::emitFunction(FunctionNode* funNode, bool needsProto)
         if (!script)
             return false;
 
+        FieldInitializers fieldInitializers = FieldInitializers::Invalid();
+        if (classContentsIfConstructor) {
+            fieldInitializers = setupFieldInitializers(classContentsIfConstructor);
+        }
+
         BytecodeEmitter bce2(this, parser, funbox, script, /* lazyScript = */ nullptr,
-                             funNode->pn_pos, emitterMode);
+                             funNode->pn_pos, emitterMode, fieldInitializers);
         if (!bce2.init())
             return false;
 
@@ -5660,6 +5679,8 @@ BytecodeEmitter::emitFunction(FunctionNode* funNode, bool needsProto)
         if (!bce2.emitFunctionScript(funNode))
             return false;
 
+        // fieldInitializers are copied to the JSScript inside BytecodeEmitter
+
         if (funbox->isLikelyConstructorWrapper()) {
             script->setLikelyConstructorWrapper();
         }
@@ -7932,7 +7953,7 @@ BytecodeEmitter::emitCreateFieldKeys(ListNode* obj)
 bool
 BytecodeEmitter::emitCreateFieldInitializers(ListNode* obj)
 {
-    const FieldInitializers& fieldInitializers = fieldInitializers_;
+    FieldInitializers fieldInitializers = setupFieldInitializers(obj);
     MOZ_ASSERT(fieldInitializers.valid);
     size_t numFields = fieldInitializers.numFieldInitializers;
 
@@ -7989,6 +8010,132 @@ BytecodeEmitter::emitCreateFieldInitializers(ListNode* obj)
     return true;
 }
 
+const FieldInitializers&
+BytecodeEmitter::findFieldInitializersForCall()
+{
+  for (BytecodeEmitter* current = this; current; current = current->parent) {
+      if (current->sc->isFunctionBox()) {
+          FunctionBox* box = current->sc->asFunctionBox();
+          if (box->function()->kind() == JSFunction::FunctionKind::ClassConstructor) {
+              const FieldInitializers& fieldInitializers = current->getFieldInitializers();
+              MOZ_ASSERT(fieldInitializers.valid);
+              return fieldInitializers;
+          }
+      }
+  }
+
+  for (ScopeIter si(innermostScope()); si; si++) {
+      if (si.scope()->is<FunctionScope>()) {
+          JSFunction* fun = si.scope()->as<FunctionScope>().canonicalFunction();
+          if (fun->kind() == JSFunction::FunctionKind::ClassConstructor) {
+              const FieldInitializers& fieldInitializers = fun->isInterpretedLazy()
+                                                ? fun->lazyScript()->getFieldInitializers()
+                                                : fun->nonLazyScript()->getFieldInitializers();
+              MOZ_ASSERT(fieldInitializers.valid);
+              return fieldInitializers;
+          }
+      }
+  }
+
+  MOZ_CRASH("Constructor for field initializers not found.");
+}
+
+bool
+BytecodeEmitter::emitCopyInitializersToLocalInitializers()
+{
+    MOZ_ASSERT(sc->asFunctionBox()->isDerivedClassConstructor());
+    if (getFieldInitializers().numFieldInitializers == 0)
+      return true;
+
+    NameOpEmitter noe(this, cx->names().dotLocalInitializers, NameOpEmitter::Kind::Initialize);
+    if (!noe.prepareForRhs()) {
+        //              [stack]
+        return false;
+    }
+
+    if (!emitGetName(cx->names().dotInitializers)) {
+        //              [stack] .initializers
+        return false;
+    }
+
+    if (!noe.emitAssignment()) {
+        //              [stack] .initializers
+        return false;
+    }
+
+    if (!emit1(JSOP_POP)) {
+        //              [stack]
+        return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitInitializeInstanceFields(bool isSuperCall)
+{
+    const FieldInitializers& fieldInitializers = findFieldInitializersForCall();
+    size_t numFields = fieldInitializers.numFieldInitializers;
+
+    if (numFields == 0) {
+      return true;
+    }
+
+    if (isSuperCall) {
+        if (!emitGetName(cx->names().dotLocalInitializers)) {
+            //              [stack] ARRAY
+            return false;
+        }
+    } else {
+        if (!emitGetName(cx->names().dotInitializers)) {
+            //              [stack] ARRAY
+            return false;
+        }
+    }
+
+    for (size_t fieldIndex = 0; fieldIndex < numFields; fieldIndex++) {
+      if (fieldIndex < numFields - 1) {
+        // We DUP to keep the array around (it is consumed in the bytecode below)
+        // for next iterations of this loop, except for the last iteration, which
+        // avoids an extra POP at the end of the loop.
+        if (!emit1(JSOP_DUP)) {
+          //          [stack] ARRAY ARRAY
+          return false;
+        }
+      }
+
+      if (!emitNumberOp(fieldIndex)) {
+        //            [stack] ARRAY? ARRAY INDEX
+        return false;
+      }
+
+      // Don't use CALLELEM here, because the receiver of the call != the receiver
+      // of this getelem. (Specifically, the call receiver is `this`, and the
+      // receiver of this getelem is `.initializers`)
+      if (!emit1(JSOP_GETELEM)) {
+        //            [stack] ARRAY? FUNC
+        return false;
+      }
+
+      // This is guaranteed to run after super(), so we don't need TDZ checks.
+      if (!emitGetName(cx->names().dotThis)) {
+        //            [stack] ARRAY? FUNC THIS
+        return false;
+      }
+
+      if (!emitCall(JSOP_CALL_IGNORES_RV, 0)) {
+        //            [stack] ARRAY? RVAL
+        return false;
+      }
+
+      if (!emit1(JSOP_POP)) {
+        //            [stack] ARRAY?
+        return false;
+      }
+    }
+
+    return true;
+}
 
 // Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See
 // the comment on emitSwitch.
@@ -8446,20 +8593,6 @@ BytecodeEmitter::emitLexicalInitialization(JSAtom* name)
 
     return true;
 }
-class AutoResetFieldInitializers
-{
-    BytecodeEmitter* bce;
-    FieldInitializers oldFieldInfo;
-
-  public:
-    AutoResetFieldInitializers(BytecodeEmitter* bce, FieldInitializers newFieldInfo)
-      : bce(bce), oldFieldInfo(bce->fieldInitializers_)
-    {
-        bce->fieldInitializers_ = newFieldInfo;
-    }
-
-    ~AutoResetFieldInitializers() { bce->fieldInitializers_ = oldFieldInfo; }
-};
 
 // This follows ES6 14.5.14 (ClassDefinitionEvaluation) and ES6 14.5.15
 // (BindingClassDeclarationEvaluation).
@@ -8485,15 +8618,11 @@ BytecodeEmitter::emitClass(ClassNode* classNode)
         }
     }
 
-    // set this->fieldInitializers_
-    AutoResetFieldInitializers _innermostClassAutoReset(this, setupFieldInitializers(classMembers));
-
     //                [stack]
 
     ClassEmitter ce(this);
     RootedAtom innerName(cx);
     ClassEmitter::Kind kind = ClassEmitter::Kind::Expression;
-
     if (names) {
         innerName = names->innerBinding()->as<NameNode>().atom();
         MOZ_ASSERT(innerName);
@@ -8503,8 +8632,10 @@ BytecodeEmitter::emitClass(ClassNode* classNode)
             MOZ_ASSERT(names->outerBinding()->as<NameNode>().atom() == innerName);
             kind = ClassEmitter::Kind::Declaration;
         }
+    }
 
-        if (!ce.emitScopeForNamedClass(classNode->scopeBindings())) {
+    if (!classNode->isEmptyScope()) {
+        if (!ce.emitScope(classNode->scopeBindings(), classNode->names() != nullptr)) {
             //            [stack]
             return false;
         }
@@ -8534,7 +8665,7 @@ BytecodeEmitter::emitClass(ClassNode* classNode)
     if (constructor) {
         bool needsHomeObject = constructor->funbox()->needsHomeObject();
         // HERITAGE is consumed inside emitFunction.
-        if (!emitFunction(constructor, isDerived)) {
+        if (!emitFunction(constructor, isDerived, classMembers)) {
             //          [stack] HOMEOBJ CTOR
             return false;
         }
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 42faa78007..8a196a4799 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -181,6 +181,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
 
     /* field info for enclosing class */
     FieldInitializers fieldInitializers_;
+    const FieldInitializers& getFieldInitializers() { return fieldInitializers_; }
 
 #ifdef DEBUG
     bool unstableEmitterScope;
@@ -251,13 +252,15 @@ struct MOZ_STACK_CLASS BytecodeEmitter
      */
     BytecodeEmitter(BytecodeEmitter* parent, Parser<FullParseHandler>* parser, SharedContext* sc,
                     HandleScript script, Handle<LazyScript*> lazyScript, uint32_t lineNum,
-                    EmitterMode emitterMode = Normal);
+                    EmitterMode emitterMode = Normal,
+                    FieldInitializers fieldInitializers = FieldInitializers::Invalid());
 
     // An alternate constructor that uses a TokenPos for the starting
     // line and that sets functionBodyEndPos as well.
     BytecodeEmitter(BytecodeEmitter* parent, Parser<FullParseHandler>* parser, SharedContext* sc,
                     HandleScript script, Handle<LazyScript*> lazyScript,
-                    TokenPos bodyPosition, EmitterMode emitterMode = Normal);
+                    TokenPos bodyPosition, EmitterMode emitterMode = Normal,
+                    FieldInitializers fieldInitializers = FieldInitializers::Invalid());
 
     MOZ_MUST_USE bool init();
 
@@ -514,7 +517,9 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     MOZ_MUST_USE bool emitObjectPairOp(ObjectBox* objbox1, ObjectBox* objbox2, JSOp op);
     MOZ_MUST_USE bool emitRegExp(uint32_t index);
 
-    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitFunction(FunctionNode* funNode, bool needsProto = false);
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitFunction(FunctionNode* funNode,
+                                                    bool needsProto = false,
+                                                    ListNode* classContentsIfConstructor = nullptr);
     MOZ_NEVER_INLINE MOZ_MUST_USE bool emitObject(ListNode* objNode);
 
     MOZ_MUST_USE bool replaceNewInitWithNewObject(JSObject* obj, ptrdiff_t offset);
@@ -527,6 +532,9 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     FieldInitializers setupFieldInitializers(ListNode* classMembers);
     MOZ_MUST_USE bool emitCreateFieldKeys(ListNode* obj);
     MOZ_MUST_USE bool emitCreateFieldInitializers(ListNode* obj);
+    const FieldInitializers& findFieldInitializersForCall();
+    MOZ_MUST_USE bool emitCopyInitializersToLocalInitializers();
+    MOZ_MUST_USE bool emitInitializeInstanceFields(bool isSuperCall);
 
     // To catch accidental misuse, emitUint16Operand/emit3 assert that they are
     // not used to unconditionally emit JSOP_GETLOCAL. Variable access should
diff --git a/js/src/frontend/FullParseHandler.h b/js/src/frontend/FullParseHandler.h
index 3f52e88d54..d8ac80e2c6 100644
--- a/js/src/frontend/FullParseHandler.h
+++ b/js/src/frontend/FullParseHandler.h
@@ -367,7 +367,9 @@ FOR_EACH_PARSENODE_SUBCLASS(DECLARE_AS)
         return literal;
     }
 
-    ClassNodeType newClass(Node name, Node heritage, Node memberBlock, const TokenPos& pos) {
+    ClassNodeType newClass(Node name, Node heritage, LexicalScopeNodeType memberBlock,
+                           const TokenPos& pos)
+    {
         return new_<ClassNode>(name, heritage, memberBlock, pos);
     }
     ListNodeType newClassMemberList(uint32_t begin) {
diff --git a/js/src/frontend/FunctionEmitter.cpp b/js/src/frontend/FunctionEmitter.cpp
index f9e8faf714..98dffe6b04 100644
--- a/js/src/frontend/FunctionEmitter.cpp
+++ b/js/src/frontend/FunctionEmitter.cpp
@@ -477,9 +477,16 @@ bool FunctionScriptEmitter::prepareForBody()
     }
 
     if (funbox_->function()->kind() == JSFunction::FunctionKind::ClassConstructor) {
-        if (!emitInitializeInstanceFields()) {
-            //        [stack]
-            return false;
+        if (funbox_->isDerivedClassConstructor()) {
+            if (!bce_->emitCopyInitializersToLocalInitializers()) {
+                //        [stack]
+                return false;
+            }
+        } else {
+            if (!bce_->emitInitializeInstanceFields(false)) {
+                //        [stack]
+                return false;
+            }
         }
     }
 
@@ -551,64 +558,6 @@ bool FunctionScriptEmitter::emitExtraBodyVarScope()
     return true;
 }
 
-bool FunctionScriptEmitter::emitInitializeInstanceFields()
-{
-    MOZ_ASSERT(bce_->fieldInitializers_.valid);
-    size_t numFields = bce_->fieldInitializers_.numFieldInitializers;
-
-    if (numFields == 0) {
-        return true;
-    }
-
-    if (!bce_->emitGetName(bce_->cx->names().dotInitializers)) {
-        //              [stack] ARRAY
-        return false;
-    }
-
-    for (size_t fieldIndex = 0; fieldIndex < numFields; fieldIndex++) {
-        if (fieldIndex < numFields - 1) {
-            // We DUP to keep the array around (it is consumed in the bytecode below)
-            // for next iterations of this loop, except for the last iteration, which
-            // avoids an extra POP at the end of the loop.
-            if (!bce_->emit1(JSOP_DUP)) {
-                //          [stack] ARRAY ARRAY
-                return false;
-            }
-        }
-
-        if (!bce_->emitNumberOp(fieldIndex)) {
-            //            [stack] ARRAY? ARRAY INDEX
-            return false;
-        }
-
-        // Don't use CALLELEM here, because the receiver of the call != the receiver
-        // of this getelem. (Specifically, the call receiver is `this`, and the
-        // receiver of this getelem is `.initializers`)
-        if (!bce_->emit1(JSOP_GETELEM)) {
-            //            [stack] ARRAY? FUNC
-            return false;
-        }
-
-        // This is guaranteed to run after super(), so we don't need TDZ checks.
-        if (!bce_->emitGetName(bce_->cx->names().dotThis)) {
-            //            [stack] ARRAY? FUNC THIS
-            return false;
-        }
-
-        if (!bce_->emitCall(JSOP_CALL_IGNORES_RV, 0)) {
-            //            [stack] ARRAY? RVAL
-            return false;
-        }
-
-        if (!bce_->emit1(JSOP_POP)) {
-            //            [stack] ARRAY?
-            return false;
-        }
-    }
-
-    return true;
-}
-
 bool FunctionScriptEmitter::emitEndBody()
 {
     MOZ_ASSERT(state_ == State::Body);
diff --git a/js/src/frontend/FunctionEmitter.h b/js/src/frontend/FunctionEmitter.h
index ce068c6b56..98d0ad1bb5 100644
--- a/js/src/frontend/FunctionEmitter.h
+++ b/js/src/frontend/FunctionEmitter.h
@@ -257,7 +257,6 @@ class MOZ_STACK_CLASS FunctionScriptEmitter {
 
  private:
     MOZ_MUST_USE bool emitExtraBodyVarScope();
-    MOZ_MUST_USE bool emitInitializeInstanceFields();
 };
 
 // Class for emitting function parameters.
diff --git a/js/src/frontend/ObjectEmitter.cpp b/js/src/frontend/ObjectEmitter.cpp
index b89596a774..f421030e99 100644
--- a/js/src/frontend/ObjectEmitter.cpp
+++ b/js/src/frontend/ObjectEmitter.cpp
@@ -531,14 +531,16 @@ ClassEmitter::ClassEmitter(BytecodeEmitter* bce)
     isClass_ = true;
 }
 
-bool ClassEmitter::emitScopeForNamedClass(JS::Handle<LexicalScope::Data*> scopeBindings)
+bool ClassEmitter::emitScope(JS::Handle<LexicalScope::Data*> scopeBindings, bool hasName)
 {
     MOZ_ASSERT(propertyState_ == PropertyState::Start);
     MOZ_ASSERT(classState_ == ClassState::Start);
 
-    tdzCacheForInnerName_.emplace(bce_);
-    innerNameScope_.emplace(bce_);
-    if (!innerNameScope_->enterLexical(bce_, ScopeKind::Lexical, scopeBindings))
+    if (hasName)
+        tdzCacheForInnerName_.emplace(bce_);
+
+    innerScope_.emplace(bce_);
+    if (!innerScope_->enterLexical(bce_, ScopeKind::Lexical, scopeBindings))
         return false;
 
 #ifdef DEBUG
@@ -716,7 +718,7 @@ bool ClassEmitter::emitEnd(Kind kind)
 
     if (name_ != bce_->cx->names().empty) {
         MOZ_ASSERT(tdzCacheForInnerName_.isSome());
-        MOZ_ASSERT(innerNameScope_.isSome());
+        MOZ_ASSERT(innerScope_.isSome());
 
         if (!bce_->emitLexicalInitialization(name_)) {
             //            [stack] CTOR
@@ -724,9 +726,9 @@ bool ClassEmitter::emitEnd(Kind kind)
         }
 
         // Pop the inner scope.
-        if (!innerNameScope_->leave(bce_))
+        if (!innerScope_->leave(bce_))
             return false;
-        innerNameScope_.reset();
+        innerScope_.reset();
 
         if (kind == Kind::Declaration) {
             if (!bce_->emitLexicalInitialization(name_)) {
@@ -742,9 +744,18 @@ bool ClassEmitter::emitEnd(Kind kind)
         }
 
         tdzCacheForInnerName_.reset();
-    } else {
+    } else if (innerScope_.isSome()) {
+        //              [stack] CTOR
+        MOZ_ASSERT(kind == Kind::Expression);
+        MOZ_ASSERT(tdzCacheForInnerName_.isNothing());
+
+        if (!innerScope_->leave(bce_))
+            return false;
+        innerScope_.reset();
+    }else {
         //              [stack] CTOR
 
+        MOZ_ASSERT(kind == Kind::Expression);
         MOZ_ASSERT(tdzCacheForInnerName_.isNothing());
     }
 
diff --git a/js/src/frontend/ObjectEmitter.h b/js/src/frontend/ObjectEmitter.h
index 85a6f81faa..952d4cf156 100644
--- a/js/src/frontend/ObjectEmitter.h
+++ b/js/src/frontend/ObjectEmitter.h
@@ -464,6 +464,7 @@ class MOZ_RAII AutoSaveLocalStrictMode
 //
 //   `class {}`
 //     ClassEmitter ce(this);
+//     ce.emitScope(scopeBindings, false);
 //     ce.emitClass();
 //
 //     ce.emitInitDefaultConstructor(Some(offset_of_class),
@@ -473,6 +474,7 @@ class MOZ_RAII AutoSaveLocalStrictMode
 //
 //   `class { constructor() { ... } }`
 //     ClassEmitter ce(this);
+//     ce.emitScope(scopeBindings, false);
 //     ce.emitClass();
 //
 //     emit(function_for_constructor);
@@ -482,7 +484,7 @@ class MOZ_RAII AutoSaveLocalStrictMode
 //
 //   `class X { constructor() { ... } }`
 //     ClassEmitter ce(this);
-//     ce.emitScopeForNamedClass(scopeBindingForName);
+//     ce.emitScope(scopeBindings, true);
 //     ce.emitClass(atom_of_X);
 //
 //     ce.emitInitDefaultConstructor(Some(offset_of_class),
@@ -492,7 +494,7 @@ class MOZ_RAII AutoSaveLocalStrictMode
 //
 //   `class X { constructor() { ... } }`
 //     ClassEmitter ce(this);
-//     ce.emitScopeForNamedClass(scopeBindingForName);
+//     ce.emitScope(scopeBindings, true);
 //     ce.emitClass(atom_of_X);
 //
 //     emit(function_for_constructor);
@@ -502,7 +504,7 @@ class MOZ_RAII AutoSaveLocalStrictMode
 //
 //   `class X extends Y { constructor() { ... } }`
 //     ClassEmitter ce(this);
-//     ce.emitScopeForNamedClass(scopeBindingForName);
+//     ce.emitScope(scopeBindings, true);
 //
 //     emit(Y);
 //     ce.emitDerivedClass(atom_of_X);
@@ -514,7 +516,7 @@ class MOZ_RAII AutoSaveLocalStrictMode
 //
 //   `class X extends Y { constructor() { ... super.f(); ... } }`
 //     ClassEmitter ce(this);
-//     ce.emitScopeForNamedClass(scopeBindingForName);
+//     ce.emitScope(scopeBindings, true);
 //
 //     emit(Y);
 //     ce.emitDerivedClass(atom_of_X);
@@ -629,21 +631,21 @@ class MOZ_STACK_CLASS ClassEmitter : public PropertyEmitter
     bool isDerived_ = false;
 
     mozilla::Maybe<TDZCheckCache> tdzCacheForInnerName_;
-    mozilla::Maybe<EmitterScope> innerNameScope_;
+    mozilla::Maybe<EmitterScope> innerScope_;
     AutoSaveLocalStrictMode strictMode_;
 
 #ifdef DEBUG
     // The state of this emitter.
     //
     // +-------+
-    // | Start |-+------------------------------------>+-+
-    // +-------+ |                                     ^ |
-    //           | [named class]                       | |
-    //           |   emitScopeForNamedClass  +-------+ | |
-    //           +-------------------------->| Scope |-+ |
-    //                                       +-------+   |
-    //                                                   |
-    //   +-----------------------------------------------+
+    // | Start |-+------------------------>+-+
+    // +-------+ |                         ^ |
+    //           | [has scope]             | |
+    //           |   emitScope   +-------+ | |
+    //           +-------------->| Scope |-+ |
+    //                           +-------+   |
+    //                                       |
+    //   +-----------------------------------+
     //   |
     //   |   emitClass           +-------+
     //   +-+----------------->+->| Class |-+
@@ -669,7 +671,7 @@ class MOZ_STACK_CLASS ClassEmitter : public PropertyEmitter
         // The initial state.
         Start,
 
-        // After calling emitScopeForNamedClass.
+        // After calling emitScope.
         Scope,
 
         // After calling emitClass or emitDerivedClass.
@@ -689,8 +691,7 @@ class MOZ_STACK_CLASS ClassEmitter : public PropertyEmitter
   public:
     explicit ClassEmitter(BytecodeEmitter* bce);
 
-    MOZ_MUST_USE bool emitScopeForNamedClass(
-        JS::Handle<LexicalScope::Data*> scopeBindings);
+    MOZ_MUST_USE bool emitScope(JS::Handle<LexicalScope::Data*> scopeBindings, bool hasName);
 
     // @param name
     //        Name of the class (nullptr if this is anonymous class)
diff --git a/js/src/frontend/ParseNode.h b/js/src/frontend/ParseNode.h
index fffda6a73d..da722a51e7 100644
--- a/js/src/frontend/ParseNode.h
+++ b/js/src/frontend/ParseNode.h
@@ -252,10 +252,7 @@ IsTypeofKind(ParseNodeKind kind)
  * PNK_CLASS (ClassNode)
  *   kid1: PNK_CLASSNAMES for class name. can be null for anonymous class.
  *   kid2: expression after `extends`. null if no expression
- *   kid3: either of
- *           * PNK_CLASSMEMBERLIST, if anonymous class
- *           * PNK_LEXICALSCOPE which contains PNK_CLASSMEMBERLIST as scopeBody,
- *             if named class
+ *   kid3: PNK_LEXICALSCOPE which contains PNK_CLASSMEMBERLIST as scopeBody
  * PNK_CLASSNAMES (ClassNames)
  *   left: Name node for outer binding, or null if the class is an expression
  *         that doesn't create an outer binding
@@ -2243,13 +2240,11 @@ class ClassNames : public BinaryNode
 class ClassNode : public TernaryNode
 {
   public:
-    ClassNode(ParseNode* names, ParseNode* heritage, ParseNode* membersOrBlock,
+    ClassNode(ParseNode* names, ParseNode* heritage, LexicalScopeNode* memberBlock,
               const TokenPos& pos)
-      : TernaryNode(PNK_CLASS, JSOP_NOP, names, heritage, membersOrBlock, pos)
+      : TernaryNode(PNK_CLASS, JSOP_NOP, names, heritage, memberBlock, pos)
     {
         MOZ_ASSERT_IF(names, names->is<ClassNames>());
-        MOZ_ASSERT(membersOrBlock->is<LexicalScopeNode>() ||
-                   membersOrBlock->isKind(PNK_CLASSMEMBERLIST));
     }
 
     static bool test(const ParseNode& node) {
@@ -2265,14 +2260,14 @@ class ClassNode : public TernaryNode
         return kid2();
     }
     ListNode* memberList() const {
-        ParseNode* membersOrBlock = kid3();
-        if (membersOrBlock->isKind(PNK_CLASSMEMBERLIST))
-            return &membersOrBlock->as<ListNode>();
-
-        ListNode* list = &membersOrBlock->as<LexicalScopeNode>().scopeBody()->as<ListNode>();
+        ListNode* list = &kid3()->as<LexicalScopeNode>().scopeBody()->as<ListNode>();
         MOZ_ASSERT(list->isKind(PNK_CLASSMEMBERLIST));
         return list;
     }
+    bool isEmptyScope() const {
+        ParseNode* scope = kid3();
+        return scope->as<LexicalScopeNode>().isEmptyScope();
+    }
     Handle<LexicalScope::Data*> scopeBindings() const {
         ParseNode* scope = kid3();
         return scope->as<LexicalScopeNode>().scopeBindings();
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index 77fa337fb7..8e09aea626 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -2779,6 +2779,12 @@ Parser<ParseHandler>::functionBody(InHandling inHandling, YieldHandling yieldHan
             return null();
     }
 
+    if (kind == FunctionSyntaxKind::DerivedClassConstructor) {
+        if (!noteDeclaredName(context->names().dotLocalInitializers,
+                              DeclarationKind::Var, pos()))
+            return null();
+    }
+
     return finishLexicalScope(pc->varScope(), body);
 }
 
@@ -3600,7 +3606,11 @@ Parser<FullParseHandler>::standaloneLazyFunction(HandleFunction fun, bool strict
 
     FunctionSyntaxKind syntaxKind = FunctionSyntaxKind::Statement;
     if (fun->isClassConstructor()) {
-        syntaxKind = FunctionSyntaxKind::ClassConstructor;
+        if (fun->isDerivedClassConstructor()) {
+            syntaxKind = FunctionSyntaxKind::DerivedClassConstructor;
+        } else {
+            syntaxKind = FunctionSyntaxKind::ClassConstructor;
+        }
     } else if (fun->isMethod()) {
         syntaxKind = FunctionSyntaxKind::Method;
     } else if (fun->isGetter()) {
@@ -7468,7 +7478,7 @@ Parser<ParseHandler>::classMember(YieldHandling yieldHandling, DefaultHandling d
 
         numFields++;
 
-        FunctionNodeType initializer = fieldInitializerOpt(yieldHandling, hasHeritage, propName,
+        FunctionNodeType initializer = fieldInitializerOpt(yieldHandling, hasHeritage,
                                                            propAtom, numFieldKeys);
         if (!initializer)
             return false;
@@ -7553,8 +7563,9 @@ Parser<ParseHandler>::classMember(YieldHandling yieldHandling, DefaultHandling d
 template <typename ParseHandler>
 bool
 Parser<ParseHandler>::finishClassConstructor(const ParseContext::ClassStatement& classStmt,
-                                             HandlePropertyName className, uint32_t classStartOffset,
-                                             uint32_t classEndOffset, size_t numFields,
+                                             HandlePropertyName className, bool hasHeritage,
+                                             uint32_t classStartOffset, uint32_t classEndOffset,
+                                             size_t numFields,
                                              ListNodeType& classMembers)
 {
     // Fields cannot re-use the constructor obtained via JSOP_CLASSCONSTRUCTOR or
@@ -7562,7 +7573,7 @@ Parser<ParseHandler>::finishClassConstructor(const ParseContext::ClassStatement&
     // initializers in the constructor. So, synthesize a new one.
     if (classStmt.constructorBox == nullptr && numFields > 0) {
         // synthesizeConstructor assigns to classStmt.constructorBox
-        FunctionNodeType synthesizedCtor = synthesizeConstructor(className, classStartOffset);
+        FunctionNodeType synthesizedCtor = synthesizeConstructor(className, classStartOffset, hasHeritage);
         if (!synthesizedCtor) {
             return false;
         }
@@ -7600,12 +7611,6 @@ Parser<ParseHandler>::finishClassConstructor(const ParseContext::ClassStatement&
             if (numFields > 0) {
                 ctorbox->function()->lazyScript()->setHasThisBinding();
             }
-
-            // Field initializers can be retrieved if the class and constructor are
-            // being compiled at the same time, but we need to stash the field
-            // information if the constructor is being compiled lazily.
-            FieldInitializers fieldInfo(numFields);
-            ctorbox->function()->lazyScript()->setFieldInitializers(fieldInfo);
         }
     }
 
@@ -7724,7 +7729,7 @@ Parser<ParseHandler>::classDefinition(YieldHandling yieldHandling,
                                                   pc->innermostScope()->id()))
                 return null();
             if (!noteDeclaredName(context->names().dotInitializers,
-                                  DeclarationKind::Var, namePos))
+                                  DeclarationKind::Let, namePos))
                 return null();
         }
 
@@ -7733,8 +7738,8 @@ Parser<ParseHandler>::classDefinition(YieldHandling yieldHandling,
                 return null();
         }
         classEndOffset = pos().end;
-        if (!finishClassConstructor(classStmt, className, classStartOffset,
-                                    classEndOffset, numFields, classMembers))
+        if (!finishClassConstructor(classStmt, className, hasHeritage,
+                                    classStartOffset, classEndOffset, numFields, classMembers))
             return null();
 
         if (className) {
@@ -7779,9 +7784,10 @@ Parser<ParseHandler>::classDefinition(YieldHandling yieldHandling,
 
 template <class ParseHandler>
 typename ParseHandler::FunctionNodeType
-Parser<ParseHandler>::synthesizeConstructor(HandleAtom className, uint32_t classNameOffset)
+Parser<ParseHandler>::synthesizeConstructor(HandleAtom className, uint32_t classNameOffset, bool hasHeritage)
 {
-    FunctionSyntaxKind functionSyntaxKind = FunctionSyntaxKind::ClassConstructor;
+    FunctionSyntaxKind functionSyntaxKind = hasHeritage ? FunctionSyntaxKind::DerivedClassConstructor
+                                                        : FunctionSyntaxKind::ClassConstructor;
 
     // Create the function object.
     RootedFunction fun(context, newFunction(className, functionSyntaxKind,
@@ -7820,6 +7826,8 @@ Parser<ParseHandler>::synthesizeConstructor(HandleAtom className, uint32_t class
     funbox->function()->setArgCount(0);
     funbox->setStart(tokenStream);
 
+    pc->functionScope().useAsVarScope(pc);
+
     // Push a LexicalScope on to the stack.
     ParseContext::Scope lexicalScope(this);
     if (!lexicalScope.init(pc))
@@ -7835,10 +7843,55 @@ Parser<ParseHandler>::synthesizeConstructor(HandleAtom className, uint32_t class
     // One might expect a noteUsedName(".initializers") here. See comment in
     // GeneralParser<ParseHandler, Unit>::classDefinition on why it's not here.
 
+    if (hasHeritage) {
+        if (!noteDeclaredName(context->names().dotLocalInitializers,
+                              DeclarationKind::Var, synthesizedBodyPos))
+            return null();
+    }
+
     bool canSkipLazyClosedOverBindings = handler.canSkipLazyClosedOverBindings();
     if (!declareFunctionThis(canSkipLazyClosedOverBindings))
         return null();
 
+    if (hasHeritage) {
+        // {Goanna} Need a different this-NameNode for SuperBase and SetThis or the recycling
+        //          by ParseNodeAllocator runs into all sorts of problems because the
+        //          same ParseNode gets cleaned up twice.
+        //          Parser<ParseHandler>::memberExpr does the same.
+        NameNodeType thisNameBase = newThisName();
+        if (!thisNameBase)
+            return null();
+
+        UnaryNodeType superBase = handler.newSuperBase(thisNameBase, synthesizedBodyPos);
+        if (!superBase)
+            return null();
+
+        ListNodeType arguments = handler.newArguments(synthesizedBodyPos);
+        if (!arguments)
+            return null();
+
+        BinaryNodeType superCall = handler.newSuperCall(superBase, arguments, false);
+        if (!superCall)
+            return null();
+
+        NameNodeType thisName = newThisName();
+        if (!thisName)
+            return null();
+
+        BinaryNodeType setThis = handler.newSetThis(thisName, superCall);
+        if (!setThis)
+            return null();
+
+        if (!noteUsedName(context->names().dotLocalInitializers))
+          return null();
+
+        UnaryNodeType exprStatement = handler.newExprStatement(setThis, synthesizedBodyPos.end);
+        if (!exprStatement)
+            return null();
+
+        handler.addStatementToList(stmtList, exprStatement);
+    }
+
     auto initializerBody = finishLexicalScope(lexicalScope, stmtList);
     if (!initializerBody)
         return null();
@@ -7860,7 +7913,7 @@ Parser<ParseHandler>::synthesizeConstructor(HandleAtom className, uint32_t class
 template <class ParseHandler>
 typename ParseHandler::FunctionNodeType
 Parser<ParseHandler>::fieldInitializerOpt(YieldHandling yieldHandling, bool hasHeritage,
-                                          Node propName, HandleAtom propAtom, size_t& numFieldKeys)
+                                          HandleAtom propAtom, size_t& numFieldKeys)
 {
     bool hasInitializer = false;
     if (!tokenStream.matchToken(&hasInitializer, TOK_ASSIGN))
@@ -7878,9 +7931,9 @@ Parser<ParseHandler>::fieldInitializerOpt(YieldHandling yieldHandling, bool hasH
         firstTokenPos = TokenPos(endPos, endPos);
     }
 
-    // Create the function object.
+    // Create the anonymous function object.
     RootedFunction fun(context,
-                       newFunction(propAtom, FunctionSyntaxKind::Expression,
+                       newFunction(nullptr, FunctionSyntaxKind::Expression,
                                    GeneratorKind::NotGenerator,
                                    FunctionAsyncKind::SyncFunction));
     if (!fun)
@@ -7981,7 +8034,12 @@ Parser<ParseHandler>::fieldInitializerOpt(YieldHandling yieldHandling, bool hasH
         if (!propAssignFieldAccess)
             return null();
     } else if (propAtom->isIndex(&indexValue)) {
-        propAssignFieldAccess = handler.newPropertyByValue(propAssignThis, propName, wholeInitializerPos.end);
+        // {Goanna} Can't reuse propName here, see comment in synthesizeConstructor
+        Node indexNode = handler.newNumber(indexValue, DecimalPoint::NoDecimal, wholeInitializerPos);
+        if (!indexNode)
+            return null();
+
+        propAssignFieldAccess = handler.newPropertyByValue(propAssignThis, indexNode, wholeInitializerPos.end);
         if (!propAssignFieldAccess)
             return null();
     } else {
@@ -9908,6 +9966,9 @@ Parser<ParseHandler>::memberExpr(YieldHandling yieldHandling, TripledotHandling
                 nextMember = handler.newSetThis(thisName, nextMember);
                 if (!nextMember)
                     return null();
+
+                if (!noteUsedName(context->names().dotLocalInitializers))
+                  return null();
             } else {
                 nextMember = memberCall(tt, lhs, yieldHandling, possibleError);
                 if (!nextMember)
diff --git a/js/src/frontend/Parser.h b/js/src/frontend/Parser.h
index f7feefcaab..5a0722afa7 100644
--- a/js/src/frontend/Parser.h
+++ b/js/src/frontend/Parser.h
@@ -1498,14 +1498,15 @@ FOR_EACH_PARSENODE_SUBCLASS(DECLARE_TYPE)
                                   ListNodeType& classMembers, bool* done);
     MOZ_MUST_USE bool finishClassConstructor(
         const ParseContext::ClassStatement& classStmt,
-        HandlePropertyName className, uint32_t classStartOffset,
-        uint32_t classEndOffset, size_t numFieldsWithInitializers,
-        ListNodeType& classMembers);
+        HandlePropertyName className, bool hasHeritage,
+        uint32_t classStartOffset, uint32_t classEndOffset,
+        size_t numFieldsWithInitializers, ListNodeType& classMembers);
 
     FunctionNodeType fieldInitializerOpt(YieldHandling yieldHandling, bool hasHeritage,
-                                         Node name, HandleAtom atom, size_t& numFieldKeys);
+                                         HandleAtom atom, size_t& numFieldKeys);
     FunctionNodeType synthesizeConstructor(HandleAtom className,
-                                           uint32_t classNameOffset);
+                                           uint32_t classNameOffset,
+                                           bool hasHeritage);
 
     bool checkLabelOrIdentifierReference(PropertyName* ident,
                                          uint32_t offset,
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index fbdd658b79..5534df5806 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -704,6 +704,35 @@ class ScriptSourceObject : public NativeObject
 enum GeneratorKind { NotGenerator, LegacyGenerator, StarGenerator };
 enum FunctionAsyncKind { SyncFunction, AsyncFunction };
 
+struct FieldInitializers
+{
+#ifdef DEBUG
+    bool valid;
+#endif
+    // This struct will eventually have a vector of constant values for optimizing
+    // field initializers.
+    size_t numFieldInitializers;
+
+    explicit FieldInitializers(size_t numFieldInitializers)
+      :
+#ifdef DEBUG
+        valid(true),
+#endif
+        numFieldInitializers(numFieldInitializers) {
+    }
+
+    static FieldInitializers Invalid() { return FieldInitializers(); }
+
+  private:
+    FieldInitializers()
+      :
+#ifdef DEBUG
+        valid(false),
+#endif
+        numFieldInitializers(0) {
+    }
+};
+
 static inline unsigned
 GeneratorKindAsBits(GeneratorKind generatorKind) {
     return static_cast<unsigned>(generatorKind);
@@ -855,6 +884,8 @@ class JSScript : public js::gc::TenuredCell
 
   private:
     js::SharedScriptData* scriptData_;
+
+    js::FieldInitializers fieldInitializers_ = js::FieldInitializers::Invalid();
   public:
     uint8_t*        data;      /* pointer to variable-length data array (see
                                    comment above Create() for details) */
@@ -1454,6 +1485,11 @@ class JSScript : public js::gc::TenuredCell
         return functionHasThisBinding_;
     }
 
+    void setFieldInitializers(js::FieldInitializers fieldInitializers) {
+        fieldInitializers_ = fieldInitializers;
+    }
+    const js::FieldInitializers& getFieldInitializers() const { return fieldInitializers_; }
+
     /*
      * Arguments access (via JSOP_*ARG* opcodes) must access the canonical
      * location for the argument. If an arguments object exists AND it's mapped
@@ -1999,35 +2035,6 @@ static_assert(sizeof(JSScript) % js::gc::CellSize == 0,
 
 namespace js {
 
-struct FieldInitializers
-{
-#ifdef DEBUG
-    bool valid;
-#endif
-    // This struct will eventually have a vector of constant values for optimizing
-    // field initializers.
-    size_t numFieldInitializers;
-
-    explicit FieldInitializers(size_t numFieldInitializers)
-      :
-#ifdef DEBUG
-        valid(true),
-#endif
-        numFieldInitializers(numFieldInitializers) {
-    }
-
-    static FieldInitializers Invalid() { return FieldInitializers(); }
-
-  private:
-    FieldInitializers()
-      :
-#ifdef DEBUG
-        valid(false),
-#endif
-        numFieldInitializers(0) {
-    }
-};
-
 // Information about a script which may be (or has been) lazily compiled to
 // bytecode from its source.
 class LazyScript : public gc::TenuredCell
@@ -2330,7 +2337,7 @@ class LazyScript : public gc::TenuredCell
         fieldInitializers_ = fieldInitializers;
     }
 
-    FieldInitializers getFieldInitializers() const { return fieldInitializers_; }
+    const FieldInitializers& getFieldInitializers() const { return fieldInitializers_; }
 
     const char* filename() const {
         return scriptSource()->filename();
diff --git a/js/src/vm/CommonPropertyNames.h b/js/src/vm/CommonPropertyNames.h
index f69dfe3ca9..bc2e4204e3 100644
--- a/js/src/vm/CommonPropertyNames.h
+++ b/js/src/vm/CommonPropertyNames.h
@@ -103,6 +103,7 @@
     macro(dotGenerator, dotGenerator, ".generator") \
     macro(dotThis, dotThis, ".this") \
     macro(dotInitializers, dotInitializers, ".initializers") \
+    macro(dotLocalInitializers, dotLocalInitializers, ".localInitializers") \
     macro(dotFieldKeys, dotFieldKeys, ".fieldKeys") \
     macro(each, each, "each") \
     macro(elementType, elementType, "elementType") \