Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -422,11 +422,12 @@
         return false;
       // Colons from ?: are handled in parseConditional().
       if (Style.Language == FormatStyle::LK_JavaScript) {
-        if (Contexts.back().ColonIsForRangeExpr ||
-            (Contexts.size() == 1 &&
+        if (Contexts.back().ColonIsForRangeExpr || // colon in for loop
+            (Contexts.size() == 1 &&               // switch/case labels
              !Line.First->isOneOf(tok::kw_enum, tok::kw_case)) ||
-            Contexts.back().ContextKind == tok::l_paren ||
-            Contexts.back().ContextKind == tok::l_square) {
+            Contexts.back().ContextKind == tok::l_paren ||  // function params
+            Contexts.back().ContextKind == tok::l_square || // array type
+            Line.MustBeDeclaration) { // method/property declaration
           Tok->Type = TT_JsTypeColon;
           break;
         }
@@ -541,6 +542,11 @@
         Tok->Type = TT_JsTypeOptionalQuestion;
         break;
       }
+      // Declarations cannot be conditional expressions, this can only be part
+      // of a type declaration.
+      if (Line.MustBeDeclaration &&
+          Style.Language == FormatStyle::LK_JavaScript)
+        break;
       parseConditional();
       break;
     case tok::kw_template:
@@ -872,7 +878,14 @@
     } else if (Current.isOneOf(tok::exclaim, tok::tilde)) {
       Current.Type = TT_UnaryOperator;
     } else if (Current.is(tok::question)) {
-      Current.Type = TT_ConditionalExpr;
+      if (Style.Language == FormatStyle::LK_JavaScript &&
+          Line.MustBeDeclaration) {
+        // In JavaScript, `interface X { foo?(): bar; }` is an optional method
+        // on the interface, not a ternary expression.
+        Current.Type = TT_JsTypeOptionalQuestion;
+      } else {
+        Current.Type = TT_ConditionalExpr;
+      }
     } else if (Current.isBinaryOperator() &&
                (!Current.Previous || Current.Previous->isNot(tok::l_square))) {
       Current.Type = TT_BinaryOperator;
@@ -1854,12 +1867,21 @@
     return Right.is(tok::coloncolon);
   if (Right.is(TT_OverloadedOperatorLParen))
     return false;
-  if (Right.is(tok::colon))
-    return !Line.First->isOneOf(tok::kw_case, tok::kw_default) &&
-           Right.getNextNonComment() && Right.isNot(TT_ObjCMethodExpr) &&
-           !Left.is(tok::question) &&
-           !(Right.is(TT_InlineASMColon) && Left.is(tok::coloncolon)) &&
-           (Right.isNot(TT_DictLiteral) || Style.SpacesInContainerLiterals);
+  if (Right.is(tok::colon)) {
+    if (Line.First->isOneOf(tok::kw_case, tok::kw_default))
+      return false;
+    if (!Right.getNextNonComment())
+      return false;
+    if (Right.is(TT_ObjCMethodExpr))
+      return false;
+    if (Left.is(tok::question))
+      return false;
+    if (Right.is(TT_InlineASMColon) && Left.is(tok::coloncolon))
+      return false;
+    if (Right.is(TT_DictLiteral))
+      return Style.SpacesInContainerLiterals;
+    return true;
+  }
   if (Left.is(TT_UnaryOperator))
     return Right.is(TT_BinaryOperator);
   if (Left.is(TT_CastRParen))
Index: lib/Format/UnwrappedLineParser.cpp
===================================================================
--- lib/Format/UnwrappedLineParser.cpp
+++ lib/Format/UnwrappedLineParser.cpp
@@ -262,9 +262,12 @@
 }
 
 void UnwrappedLineParser::parseFile() {
-  ScopedDeclarationState DeclarationState(
-      *Line, DeclarationScopeStack,
-      /*MustBeDeclaration=*/!Line->InPPDirective);
+  // The top-level context in a file always has declarations, except for pre-
+  // processor directives and JavaScript files.
+  bool MustBeDeclaration =
+      !(Line->InPPDirective || Style.Language == FormatStyle::LK_JavaScript);
+  ScopedDeclarationState DeclarationState(*Line, DeclarationScopeStack,
+                                          MustBeDeclaration);
   parseLevel(/*HasOpeningBrace=*/false);
   // Make sure to format the remaining tokens.
   flushComments(true);
@@ -845,6 +848,13 @@
         tryToParseJSFunction();
         break;
       }
+      if ((Style.Language == FormatStyle::LK_JavaScript ||
+           Style.Language == FormatStyle::LK_Java) &&
+          FormatTok->is(Keywords.kw_interface)) {
+        parseRecord();
+        break;
+      }
+
       nextToken();
       if (Line->Tokens.size() == 1 &&
           // JS doesn't have macros, and within classes colons indicate fields,
@@ -1577,7 +1587,7 @@
   // We fall through to parsing a structural element afterwards, so
   // class A {} n, m;
   // will end up in one unwrapped line.
-  // This does not apply for Java.
+  // This does not apply for Java and JavaScript.
   if (Style.Language == FormatStyle::LK_Java ||
       Style.Language == FormatStyle::LK_JavaScript)
     addUnwrappedLine();
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -703,6 +703,8 @@
                "  y?: z;\n"
                "  z?;\n"
                "}");
+  verifyFormat("interface X { y?(): z; }");
+  verifyFormat("x ? 1 : 2;");
 }
 
 TEST_F(FormatTestJS, IndexSignature) {