diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index d74f0b1df391c..b305458900de6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -10510,7 +10510,7 @@ namespace ts {
                 const signature = getSignatureFromDeclaration(node.parent);
                 const parameterIndex = node.parent.parameters.indexOf(node);
                 Debug.assert(parameterIndex >= 0);
-                return parameterIndex >= getMinArgumentCount(signature);
+                return parameterIndex >= getMinArgumentCount(signature, /*strongArityForUntypedJS*/ true);
             }
             const iife = getImmediatelyInvokedFunctionExpression(node.parent);
             if (iife) {
@@ -10601,6 +10601,9 @@ namespace ts {
                     isValueSignatureDeclaration(declaration) &&
                     !hasJSDocParameterTags(declaration) &&
                     !getJSDocType(declaration);
+                if (isUntypedSignatureInJSFile) {
+                    flags |= SignatureFlags.IsUntypedSignatureInJSFile;
+                }
 
                 // If this is a JSDoc construct signature, then skip the first parameter in the
                 // parameter list.  The first parameter represents the return type of the construct
@@ -10631,7 +10634,6 @@ namespace ts {
                     const isOptionalParameter = isOptionalJSDocParameterTag(param) ||
                         param.initializer || param.questionToken || param.dotDotDotToken ||
                         iife && parameters.length > iife.arguments.length && !type ||
-                        isUntypedSignatureInJSFile ||
                         isJSDocOptionalParameter(param);
                     if (!isOptionalParameter) {
                         minArgumentCount = parameters.length;
@@ -21107,8 +21109,10 @@ namespace ts {
                 if (isInJS && className) {
                     const classSymbol = checkExpression(className).symbol;
                     if (classSymbol && classSymbol.members && (classSymbol.flags & SymbolFlags.Function)) {
-                        const classType = (getDeclaredTypeOfSymbol(classSymbol) as InterfaceType).thisType!;
-                        return getFlowTypeOfReference(node, classType);
+                        const classType = (getDeclaredTypeOfSymbol(classSymbol) as InterfaceType).thisType;
+                        if (classType) {
+                            return getFlowTypeOfReference(node, classType);
+                        }
                     }
                 }
                 // Check if it's a constructor definition, can be either a variable decl or function decl
@@ -26377,7 +26381,7 @@ namespace ts {
             return length;
         }
 
-        function getMinArgumentCount(signature: Signature) {
+        function getMinArgumentCount(signature: Signature, strongArityForUntypedJS?: boolean) {
             if (signatureHasRestParameter(signature)) {
                 const restType = getTypeOfSymbol(signature.parameters[signature.parameters.length - 1]);
                 if (isTupleType(restType)) {
@@ -26387,6 +26391,9 @@ namespace ts {
                     }
                 }
             }
+            if (!strongArityForUntypedJS && signature.flags & SignatureFlags.IsUntypedSignatureInJSFile) {
+                return 0;
+            }
             return signature.minArgumentCount;
         }
 
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index adbe97212e2b0..356eb54165e2b 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -2273,7 +2273,7 @@ namespace ts {
 
         function emitPropertyAccessExpression(node: PropertyAccessExpression) {
             const expression = cast(emitExpression(node.expression), isExpression);
-            const token = getDotOrQuestionDotToken(node);
+            const token = node.questionDotToken || createNode(SyntaxKind.DotToken, node.expression.end, node.name.pos) as DotToken;
             const indentBeforeDot = needsIndentation(node, node.expression, token);
             const indentAfterDot = needsIndentation(node, token, node.name);
 
@@ -2289,7 +2289,12 @@ namespace ts {
                 writePunctuation(".");
             }
 
-            emitTokenWithComment(token.kind, node.expression.end, writePunctuation, node);
+            if (node.questionDotToken) {
+                emit(token);
+            }
+            else {
+                emitTokenWithComment(token.kind, node.expression.end, writePunctuation, node);
+            }
             increaseIndentIf(indentAfterDot, /*writeSpaceIfNotIndenting*/ false);
             emit(node.name);
             decreaseIndentIf(indentBeforeDot, indentAfterDot);
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 6202e5bb7eeac..557021b0e429b 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -4817,6 +4817,7 @@ namespace ts {
         HasLiteralTypes = 1 << 1,           // Indicates signature is specialized
         IsInnerCallChain = 1 << 2,          // Indicates signature comes from a CallChain nested in an outer OptionalChain
         IsOuterCallChain = 1 << 3,          // Indicates signature comes from a CallChain that is the outermost chain of an optional expression
+        IsUntypedSignatureInJSFile = 1 << 4, // Indicates signature is from a js file and has no types
 
         // We do not propagate `IsInnerCallChain` to instantiated signatures, as that would result in us
         // attempting to add `| undefined` on each recursive call to `getReturnTypeOfSignature` when
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index c0b623da1f32c..648bed6f7f9db 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -5052,10 +5052,6 @@ namespace ts {
         }
     }
 
-    export function getDotOrQuestionDotToken(node: PropertyAccessExpression) {
-        return node.questionDotToken || createNode(SyntaxKind.DotToken, node.expression.end, node.name.pos) as DotToken;
-    }
-
     export function isNamedImportsOrExports(node: Node): node is NamedImportsOrExports {
         return node.kind === SyntaxKind.NamedImports || node.kind === SyntaxKind.NamedExports;
     }
diff --git a/src/compiler/visitorPublic.ts b/src/compiler/visitorPublic.ts
index 42e3e82540092..fa611bc9bde3e 100644
--- a/src/compiler/visitorPublic.ts
+++ b/src/compiler/visitorPublic.ts
@@ -459,7 +459,7 @@ namespace ts {
                 if (node.flags & NodeFlags.OptionalChain) {
                     return updatePropertyAccessChain(<PropertyAccessChain>node,
                         visitNode((<PropertyAccessChain>node).expression, visitor, isExpression),
-                        visitNode((<PropertyAccessChain>node).questionDotToken, visitor, isToken),
+                        visitNode((<PropertyAccessChain>node).questionDotToken, tokenVisitor, isToken),
                         visitNode((<PropertyAccessChain>node).name, visitor, isIdentifier));
                 }
                 return updatePropertyAccess(<PropertyAccessExpression>node,
@@ -470,7 +470,7 @@ namespace ts {
                 if (node.flags & NodeFlags.OptionalChain) {
                     return updateElementAccessChain(<ElementAccessChain>node,
                         visitNode((<ElementAccessChain>node).expression, visitor, isExpression),
-                        visitNode((<ElementAccessChain>node).questionDotToken, visitor, isToken),
+                        visitNode((<ElementAccessChain>node).questionDotToken, tokenVisitor, isToken),
                         visitNode((<ElementAccessChain>node).argumentExpression, visitor, isExpression));
                 }
                 return updateElementAccess(<ElementAccessExpression>node,
@@ -481,7 +481,7 @@ namespace ts {
                 if (node.flags & NodeFlags.OptionalChain) {
                     return updateCallChain(<CallChain>node,
                         visitNode((<CallChain>node).expression, visitor, isExpression),
-                        visitNode((<CallChain>node).questionDotToken, visitor, isToken),
+                        visitNode((<CallChain>node).questionDotToken, tokenVisitor, isToken),
                         nodesVisitor((<CallChain>node).typeArguments, visitor, isTypeNode),
                         nodesVisitor((<CallChain>node).arguments, visitor, isExpression));
                 }
@@ -527,7 +527,7 @@ namespace ts {
                     nodesVisitor((<ArrowFunction>node).typeParameters, visitor, isTypeParameterDeclaration),
                     visitParameterList((<ArrowFunction>node).parameters, visitor, context, nodesVisitor),
                     visitNode((<ArrowFunction>node).type, visitor, isTypeNode),
-                    visitNode((<ArrowFunction>node).equalsGreaterThanToken, visitor, isToken),
+                    visitNode((<ArrowFunction>node).equalsGreaterThanToken, tokenVisitor, isToken),
                     visitFunctionBody((<ArrowFunction>node).body, visitor, context));
 
             case SyntaxKind.DeleteExpression:
@@ -558,14 +558,14 @@ namespace ts {
                 return updateBinary(<BinaryExpression>node,
                     visitNode((<BinaryExpression>node).left, visitor, isExpression),
                     visitNode((<BinaryExpression>node).right, visitor, isExpression),
-                    visitNode((<BinaryExpression>node).operatorToken, visitor, isToken));
+                    visitNode((<BinaryExpression>node).operatorToken, tokenVisitor, isToken));
 
             case SyntaxKind.ConditionalExpression:
                 return updateConditional(<ConditionalExpression>node,
                     visitNode((<ConditionalExpression>node).condition, visitor, isExpression),
-                    visitNode((<ConditionalExpression>node).questionToken, visitor, isToken),
+                    visitNode((<ConditionalExpression>node).questionToken, tokenVisitor, isToken),
                     visitNode((<ConditionalExpression>node).whenTrue, visitor, isExpression),
-                    visitNode((<ConditionalExpression>node).colonToken, visitor, isToken),
+                    visitNode((<ConditionalExpression>node).colonToken, tokenVisitor, isToken),
                     visitNode((<ConditionalExpression>node).whenFalse, visitor, isExpression));
 
             case SyntaxKind.TemplateExpression:
@@ -659,7 +659,7 @@ namespace ts {
 
             case SyntaxKind.ForOfStatement:
                 return updateForOf(<ForOfStatement>node,
-                    visitNode((<ForOfStatement>node).awaitModifier, visitor, isToken),
+                    visitNode((<ForOfStatement>node).awaitModifier, tokenVisitor, isToken),
                     visitNode((<ForOfStatement>node).initializer, visitor, isForInitializer),
                     visitNode((<ForOfStatement>node).expression, visitor, isExpression),
                     visitNode((<ForOfStatement>node).statement, visitor, isStatement, liftToBlock));
diff --git a/src/loc/lcl/esn/diagnosticMessages/diagnosticMessages.generated.json.lcl b/src/loc/lcl/esn/diagnosticMessages/diagnosticMessages.generated.json.lcl
index 9331a87553d92..369f11bae282c 100644
--- a/src/loc/lcl/esn/diagnosticMessages/diagnosticMessages.generated.json.lcl
+++ b/src/loc/lcl/esn/diagnosticMessages/diagnosticMessages.generated.json.lcl
@@ -7020,6 +7020,12 @@
         </Str>
         <Disp Icon="Str" />
       </Item>
+      <Item ItemId=";Only_named_exports_may_use_export_type_1383" ItemType="0" PsrId="306" Leaf="true">
+        <Str Cat="Text">
+          <Val><![CDATA[Only named exports may use 'export type'.]]></Val>
+        </Str>
+        <Disp Icon="Str" />
+      </Item>
       <Item ItemId=";Only_public_and_protected_methods_of_the_base_class_are_accessible_via_the_super_keyword_2340" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
           <Val><![CDATA[Only public and protected methods of the base class are accessible via the 'super' keyword.]]></Val>
@@ -7047,11 +7053,20 @@
         </Str>
         <Disp Icon="Str" />
       </Item>
-      <Item ItemId=";Option_0_can_only_be_specified_in_tsconfig_json_file_6064" ItemType="0" PsrId="306" Leaf="true">
+      <Item ItemId=";Option_0_can_only_be_specified_in_tsconfig_json_file_or_set_to_false_or_null_on_command_line_6230" ItemType="0" PsrId="306" Leaf="true">
+        <Str Cat="Text">
+          <Val><![CDATA[Option '{0}' can only be specified in 'tsconfig.json' file or set to 'false' or 'null' on command line.]]></Val>
+          <Tgt Cat="Text" Stat="Loc" Orig="New">
+            <Val><![CDATA[La opción "{0}" solo puede especificarse en el archivo "tsconfig.json" o establecerse en "false" o "null" en la línea de comandos.]]></Val>
+          </Tgt>
+        </Str>
+        <Disp Icon="Str" />
+      </Item>
+      <Item ItemId=";Option_0_can_only_be_specified_in_tsconfig_json_file_or_set_to_null_on_command_line_6064" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
-          <Val><![CDATA[Option '{0}' can only be specified in 'tsconfig.json' file.]]></Val>
+          <Val><![CDATA[Option '{0}' can only be specified in 'tsconfig.json' file or set to 'null' on command line.]]></Val>
           <Tgt Cat="Text" Stat="Loc" Orig="New">
-            <Val><![CDATA[La opción '{0}' solo se puede especificar en el archivo 'tsconfig.json'.]]></Val>
+            <Val><![CDATA[La opción "{0}" solo puede especificarse en el archivo "tsconfig.json" o establecerse en "null" en la línea de comandos.]]></Val>
           </Tgt>
         </Str>
         <Disp Icon="Str" />
@@ -9543,6 +9558,9 @@
       <Item ItemId=";Tag_0_expects_at_least_1_arguments_but_the_JSX_factory_2_provides_at_most_3_6229" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
           <Val><![CDATA[Tag '{0}' expects at least '{1}' arguments, but the JSX factory '{2}' provides at most '{3}'.]]></Val>
+          <Tgt Cat="Text" Stat="Loc" Orig="New">
+            <Val><![CDATA[La etiqueta "{0}" espera al menos "{1}" argumentos, pero el generador de JSX "{2}" proporciona como máximo "{3}".]]></Val>
+          </Tgt>
         </Str>
         <Disp Icon="Str" />
       </Item>
@@ -10869,6 +10887,12 @@
         </Str>
         <Disp Icon="Str" />
       </Item>
+      <Item ItemId=";Type_of_property_0_circularly_references_itself_in_mapped_type_1_2615" ItemType="0" PsrId="306" Leaf="true">
+        <Str Cat="Text">
+          <Val><![CDATA[Type of property '{0}' circularly references itself in mapped type '{1}'.]]></Val>
+        </Str>
+        <Disp Icon="Str" />
+      </Item>
       <Item ItemId=";Type_of_yield_operand_in_an_async_generator_must_either_be_a_valid_promise_or_must_not_contain_a_cal_1321" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
           <Val><![CDATA[Type of 'yield' operand in an async generator must either be a valid promise or must not contain a callable 'then' member.]]></Val>
diff --git a/src/loc/lcl/ita/diagnosticMessages/diagnosticMessages.generated.json.lcl b/src/loc/lcl/ita/diagnosticMessages/diagnosticMessages.generated.json.lcl
index dd6b2eddde18d..acd525bcb6be8 100644
--- a/src/loc/lcl/ita/diagnosticMessages/diagnosticMessages.generated.json.lcl
+++ b/src/loc/lcl/ita/diagnosticMessages/diagnosticMessages.generated.json.lcl
@@ -7008,6 +7008,12 @@
         </Str>
         <Disp Icon="Str" />
       </Item>
+      <Item ItemId=";Only_named_exports_may_use_export_type_1383" ItemType="0" PsrId="306" Leaf="true">
+        <Str Cat="Text">
+          <Val><![CDATA[Only named exports may use 'export type'.]]></Val>
+        </Str>
+        <Disp Icon="Str" />
+      </Item>
       <Item ItemId=";Only_public_and_protected_methods_of_the_base_class_are_accessible_via_the_super_keyword_2340" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
           <Val><![CDATA[Only public and protected methods of the base class are accessible via the 'super' keyword.]]></Val>
@@ -7035,11 +7041,20 @@
         </Str>
         <Disp Icon="Str" />
       </Item>
-      <Item ItemId=";Option_0_can_only_be_specified_in_tsconfig_json_file_6064" ItemType="0" PsrId="306" Leaf="true">
+      <Item ItemId=";Option_0_can_only_be_specified_in_tsconfig_json_file_or_set_to_false_or_null_on_command_line_6230" ItemType="0" PsrId="306" Leaf="true">
+        <Str Cat="Text">
+          <Val><![CDATA[Option '{0}' can only be specified in 'tsconfig.json' file or set to 'false' or 'null' on command line.]]></Val>
+          <Tgt Cat="Text" Stat="Loc" Orig="New">
+            <Val><![CDATA[L'opzione '{0}' può essere specificata solo nel file 'tsconfig.json' oppure impostata su 'false' o 'null' sulla riga di comando.]]></Val>
+          </Tgt>
+        </Str>
+        <Disp Icon="Str" />
+      </Item>
+      <Item ItemId=";Option_0_can_only_be_specified_in_tsconfig_json_file_or_set_to_null_on_command_line_6064" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
-          <Val><![CDATA[Option '{0}' can only be specified in 'tsconfig.json' file.]]></Val>
+          <Val><![CDATA[Option '{0}' can only be specified in 'tsconfig.json' file or set to 'null' on command line.]]></Val>
           <Tgt Cat="Text" Stat="Loc" Orig="New">
-            <Val><![CDATA[L'opzione '{0}' può essere specificata solo nel file 'tsconfig.json'.]]></Val>
+            <Val><![CDATA[L'opzione '{0}' può essere specificata solo nel file 'tsconfig.json' oppure impostata su 'null' sulla riga di comando.]]></Val>
           </Tgt>
         </Str>
         <Disp Icon="Str" />
@@ -9531,6 +9546,9 @@
       <Item ItemId=";Tag_0_expects_at_least_1_arguments_but_the_JSX_factory_2_provides_at_most_3_6229" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
           <Val><![CDATA[Tag '{0}' expects at least '{1}' arguments, but the JSX factory '{2}' provides at most '{3}'.]]></Val>
+          <Tgt Cat="Text" Stat="Loc" Orig="New">
+            <Val><![CDATA[Con il tag '{0}' sono previsti almeno '{1}' argomenti, ma la factory JSX '{2}' ne fornisce al massimo '{3}'.]]></Val>
+          </Tgt>
         </Str>
         <Disp Icon="Str" />
       </Item>
@@ -10857,6 +10875,12 @@
         </Str>
         <Disp Icon="Str" />
       </Item>
+      <Item ItemId=";Type_of_property_0_circularly_references_itself_in_mapped_type_1_2615" ItemType="0" PsrId="306" Leaf="true">
+        <Str Cat="Text">
+          <Val><![CDATA[Type of property '{0}' circularly references itself in mapped type '{1}'.]]></Val>
+        </Str>
+        <Disp Icon="Str" />
+      </Item>
       <Item ItemId=";Type_of_yield_operand_in_an_async_generator_must_either_be_a_valid_promise_or_must_not_contain_a_cal_1321" ItemType="0" PsrId="306" Leaf="true">
         <Str Cat="Text">
           <Val><![CDATA[Type of 'yield' operand in an async generator must either be a valid promise or must not contain a callable 'then' member.]]></Val>
diff --git a/src/services/textChanges.ts b/src/services/textChanges.ts
index 49f75cf41ecb4..7d424506dc39e 100644
--- a/src/services/textChanges.ts
+++ b/src/services/textChanges.ts
@@ -966,7 +966,6 @@ namespace ts.textChanges {
     function createWriter(newLine: string): TextChangesWriter {
         let lastNonTriviaPosition = 0;
 
-
         const writer = createTextWriter(newLine);
         const onEmitNode: PrintHandlers["onEmitNode"] = (hint, node, printCallback) => {
             if (node) {
diff --git a/tests/baselines/reference/allowJsClassThisTypeCrash.symbols b/tests/baselines/reference/allowJsClassThisTypeCrash.symbols
new file mode 100644
index 0000000000000..2f72ed43e2266
--- /dev/null
+++ b/tests/baselines/reference/allowJsClassThisTypeCrash.symbols
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/app.js ===
+const f = function() {};
+>f : Symbol(f, Decl(app.js, 0, 5))
+
+var g = f;
+>g : Symbol(g, Decl(app.js, 1, 3))
+>f : Symbol(f, Decl(app.js, 0, 5))
+
+g.prototype.m = function () {
+>g.prototype : Symbol(g.m, Decl(app.js, 1, 10))
+>g : Symbol(g, Decl(app.js, 1, 3))
+>prototype : Symbol(Function.prototype, Decl(lib.es5.d.ts, --, --))
+>m : Symbol(g.m, Decl(app.js, 1, 10))
+
+  this;
+};
diff --git a/tests/baselines/reference/allowJsClassThisTypeCrash.types b/tests/baselines/reference/allowJsClassThisTypeCrash.types
new file mode 100644
index 0000000000000..7c136950f3d69
--- /dev/null
+++ b/tests/baselines/reference/allowJsClassThisTypeCrash.types
@@ -0,0 +1,22 @@
+=== tests/cases/compiler/app.js ===
+const f = function() {};
+>f : () => void
+>function() {} : () => void
+
+var g = f;
+>g : () => void
+>f : () => void
+
+g.prototype.m = function () {
+>g.prototype.m = function () {  this;} : () => void
+>g.prototype.m : any
+>g.prototype : any
+>g : () => void
+>prototype : any
+>m : any
+>function () {  this;} : () => void
+
+  this;
+>this : any
+
+};
diff --git a/tests/baselines/reference/jsDeclarationsClassLeadingOptional.js b/tests/baselines/reference/jsDeclarationsClassLeadingOptional.js
new file mode 100644
index 0000000000000..a53737c1f0d29
--- /dev/null
+++ b/tests/baselines/reference/jsDeclarationsClassLeadingOptional.js
@@ -0,0 +1,27 @@
+//// [bar.js]
+export class Z {
+    f(x = 1, y) {
+        return [x, y];
+    }
+}
+
+//// [bar.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.Z = void 0;
+var Z = /** @class */ (function () {
+    function Z() {
+    }
+    Z.prototype.f = function (x, y) {
+        if (x === void 0) { x = 1; }
+        return [x, y];
+    };
+    return Z;
+}());
+exports.Z = Z;
+
+
+//// [bar.d.ts]
+export class Z {
+    f(x: number, y: any): any[];
+}
diff --git a/tests/baselines/reference/jsDeclarationsClassLeadingOptional.symbols b/tests/baselines/reference/jsDeclarationsClassLeadingOptional.symbols
new file mode 100644
index 0000000000000..15087e370eb5c
--- /dev/null
+++ b/tests/baselines/reference/jsDeclarationsClassLeadingOptional.symbols
@@ -0,0 +1,14 @@
+=== tests/cases/conformance/jsdoc/declarations/bar.js ===
+export class Z {
+>Z : Symbol(Z, Decl(bar.js, 0, 0))
+
+    f(x = 1, y) {
+>f : Symbol(Z.f, Decl(bar.js, 0, 16))
+>x : Symbol(x, Decl(bar.js, 1, 6))
+>y : Symbol(y, Decl(bar.js, 1, 12))
+
+        return [x, y];
+>x : Symbol(x, Decl(bar.js, 1, 6))
+>y : Symbol(y, Decl(bar.js, 1, 12))
+    }
+}
diff --git a/tests/baselines/reference/jsDeclarationsClassLeadingOptional.types b/tests/baselines/reference/jsDeclarationsClassLeadingOptional.types
new file mode 100644
index 0000000000000..2d4599e383648
--- /dev/null
+++ b/tests/baselines/reference/jsDeclarationsClassLeadingOptional.types
@@ -0,0 +1,16 @@
+=== tests/cases/conformance/jsdoc/declarations/bar.js ===
+export class Z {
+>Z : Z
+
+    f(x = 1, y) {
+>f : (x: number, y: any) => any[]
+>x : number
+>1 : 1
+>y : any
+
+        return [x, y];
+>[x, y] : any[]
+>x : number
+>y : any
+    }
+}
diff --git a/tests/baselines/reference/propertyAccessExpressionInnerComments.js b/tests/baselines/reference/propertyAccessExpressionInnerComments.js
index 3348c0432194d..f8a57d1c0ac55 100644
--- a/tests/baselines/reference/propertyAccessExpressionInnerComments.js
+++ b/tests/baselines/reference/propertyAccessExpressionInnerComments.js
@@ -13,6 +13,23 @@
 /*1*/Array
     // Single-line comment
     /*2*/./*3*/toString/*4*/
+
+/* Existing issue: the "2" comments below are duplicated and "3"s are missing */
+
+/*1*/Array/*2*/?./*3*/toString/*4*/
+
+/*1*/Array
+/*2*/?./*3*/
+    // Single-line comment
+    toString/*4*/
+
+/*1*/Array/*2*/?./*3*/
+    // Single-line comment
+    toString/*4*/
+
+/*1*/Array
+    // Single-line comment
+    /*2*/?./*3*/toString/*4*/
 
 
 //// [propertyAccessExpressionInnerComments.js]
@@ -27,3 +44,15 @@
 /*1*/ Array
     // Single-line comment
     /*2*/ . /*3*/toString; /*4*/
+/* Existing issue: the "2" comments below are duplicated and "3"s are missing */
+/*1*/ Array /*2*/ === null || Array /*2*/ === void 0 ? void 0 : Array /*2*/.toString; /*4*/
+/*1*/ Array === null || Array === void 0 ? void 0 : Array
+/*2*/ .
+// Single-line comment
+toString; /*4*/
+/*1*/ Array /*2*/ === null || Array /*2*/ === void 0 ? void 0 : Array /*2*/.
+// Single-line comment
+toString; /*4*/
+/*1*/ Array === null || Array === void 0 ? void 0 : Array
+// Single-line comment
+/*2*/ .toString; /*4*/
diff --git a/tests/baselines/reference/propertyAccessExpressionInnerComments.symbols b/tests/baselines/reference/propertyAccessExpressionInnerComments.symbols
index 439195f985b72..6a0ae25059eac 100644
--- a/tests/baselines/reference/propertyAccessExpressionInnerComments.symbols
+++ b/tests/baselines/reference/propertyAccessExpressionInnerComments.symbols
@@ -29,3 +29,35 @@
     /*2*/./*3*/toString/*4*/
 >toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
 
+/* Existing issue: the "2" comments below are duplicated and "3"s are missing */
+
+/*1*/Array/*2*/?./*3*/toString/*4*/
+>Array/*2*/?./*3*/toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+
+/*1*/Array
+>Array/*2*/?./*3*/    // Single-line comment    toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+/*2*/?./*3*/
+    // Single-line comment
+    toString/*4*/
+>toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+
+/*1*/Array/*2*/?./*3*/
+>Array/*2*/?./*3*/    // Single-line comment    toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    // Single-line comment
+    toString/*4*/
+>toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+
+/*1*/Array
+>Array    // Single-line comment    /*2*/?./*3*/toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    // Single-line comment
+    /*2*/?./*3*/toString/*4*/
+>toString : Symbol(Function.toString, Decl(lib.es5.d.ts, --, --))
+
diff --git a/tests/baselines/reference/propertyAccessExpressionInnerComments.types b/tests/baselines/reference/propertyAccessExpressionInnerComments.types
index 63bd06c68d4a8..d9bc3c2fa498d 100644
--- a/tests/baselines/reference/propertyAccessExpressionInnerComments.types
+++ b/tests/baselines/reference/propertyAccessExpressionInnerComments.types
@@ -29,3 +29,35 @@
     /*2*/./*3*/toString/*4*/
 >toString : () => string
 
+/* Existing issue: the "2" comments below are duplicated and "3"s are missing */
+
+/*1*/Array/*2*/?./*3*/toString/*4*/
+>Array/*2*/?./*3*/toString : () => string
+>Array : ArrayConstructor
+>toString : () => string
+
+/*1*/Array
+>Array/*2*/?./*3*/    // Single-line comment    toString : () => string
+>Array : ArrayConstructor
+
+/*2*/?./*3*/
+    // Single-line comment
+    toString/*4*/
+>toString : () => string
+
+/*1*/Array/*2*/?./*3*/
+>Array/*2*/?./*3*/    // Single-line comment    toString : () => string
+>Array : ArrayConstructor
+
+    // Single-line comment
+    toString/*4*/
+>toString : () => string
+
+/*1*/Array
+>Array    // Single-line comment    /*2*/?./*3*/toString : () => string
+>Array : ArrayConstructor
+
+    // Single-line comment
+    /*2*/?./*3*/toString/*4*/
+>toString : () => string
+
diff --git a/tests/cases/compiler/allowJsClassThisTypeCrash.ts b/tests/cases/compiler/allowJsClassThisTypeCrash.ts
new file mode 100644
index 0000000000000..bec30d8960168
--- /dev/null
+++ b/tests/cases/compiler/allowJsClassThisTypeCrash.ts
@@ -0,0 +1,10 @@
+// @checkJs: true
+// @allowJs: true
+// @noEmit: true
+
+// @filename: app.js
+const f = function() {};
+var g = f;
+g.prototype.m = function () {
+  this;
+};
\ No newline at end of file
diff --git a/tests/cases/compiler/propertyAccessExpressionInnerComments.ts b/tests/cases/compiler/propertyAccessExpressionInnerComments.ts
index f4efc986b3803..fff9401468a5b 100644
--- a/tests/cases/compiler/propertyAccessExpressionInnerComments.ts
+++ b/tests/cases/compiler/propertyAccessExpressionInnerComments.ts
@@ -12,3 +12,20 @@
 /*1*/Array
     // Single-line comment
     /*2*/./*3*/toString/*4*/
+
+/* Existing issue: the "2" comments below are duplicated and "3"s are missing */
+
+/*1*/Array/*2*/?./*3*/toString/*4*/
+
+/*1*/Array
+/*2*/?./*3*/
+    // Single-line comment
+    toString/*4*/
+
+/*1*/Array/*2*/?./*3*/
+    // Single-line comment
+    toString/*4*/
+
+/*1*/Array
+    // Single-line comment
+    /*2*/?./*3*/toString/*4*/
diff --git a/tests/cases/conformance/jsdoc/declarations/jsDeclarationsClassLeadingOptional.ts b/tests/cases/conformance/jsdoc/declarations/jsDeclarationsClassLeadingOptional.ts
new file mode 100644
index 0000000000000..b3b27f096e9a9
--- /dev/null
+++ b/tests/cases/conformance/jsdoc/declarations/jsDeclarationsClassLeadingOptional.ts
@@ -0,0 +1,11 @@
+// @allowJs: true
+// @checkJs: true
+// @target: es5
+// @outDir: ./out
+// @declaration: true
+// @filename: bar.js
+export class Z {
+    f(x = 1, y) {
+        return [x, y];
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/fourslash/extract-const2.ts b/tests/cases/fourslash/extract-const2.ts
new file mode 100644
index 0000000000000..00a9ca6ca52ba
--- /dev/null
+++ b/tests/cases/fourslash/extract-const2.ts
@@ -0,0 +1,16 @@
+/// <reference path='fourslash.ts' />
+
+////function foo(bar: number) {
+////    /*a*/bar.toString();/*b*/
+////}
+
+goTo.select("a", "b");
+edit.applyRefactor({
+    refactorName: "Extract Symbol",
+    actionName: "constant_scope_0",
+    actionDescription: "Extract to constant in enclosing scope",
+    newContent:
+`function foo(bar: number) {
+    const /*RENAME*/newLocal = bar.toString();
+}`
+});
diff --git a/tests/cases/fourslash/extract-const3.ts b/tests/cases/fourslash/extract-const3.ts
new file mode 100644
index 0000000000000..c4e79ccb746ca
--- /dev/null
+++ b/tests/cases/fourslash/extract-const3.ts
@@ -0,0 +1,18 @@
+/// <reference path='fourslash.ts' />
+
+// GH#35372
+
+////function foo(bar?: number) {
+////    /*a*/bar?.toString();/*b*/
+////}
+
+goTo.select("a", "b");
+edit.applyRefactor({
+    refactorName: "Extract Symbol",
+    actionName: "constant_scope_0",
+    actionDescription: "Extract to constant in enclosing scope",
+    newContent:
+`function foo(bar?: number) {
+    const /*RENAME*/newLocal = bar?.toString();
+}`
+});