Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -631,7 +631,7 @@
       }
       // Declarations cannot be conditional expressions, this can only be part
       // of a type declaration.
-      if (Line.MustBeDeclaration &&
+      if (Line.MustBeDeclaration && !Contexts.back().IsExpression &&
           Style.Language == FormatStyle::LK_JavaScript)
         break;
       parseConditional();
@@ -998,7 +998,7 @@
       Current.Type = TT_UnaryOperator;
     } else if (Current.is(tok::question)) {
       if (Style.Language == FormatStyle::LK_JavaScript &&
-          Line.MustBeDeclaration) {
+          Line.MustBeDeclaration && !Contexts.back().IsExpression) {
         // In JavaScript, `interface X { foo?(): bar; }` is an optional method
         // on the interface, not a ternary expression.
         Current.Type = TT_JsTypeOptionalQuestion;
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -1247,7 +1247,6 @@
   verifyFormat("interface X {\n"
                "  y?(): z;\n"
                "}");
-  verifyFormat("x ? 1 : 2;");
   verifyFormat("constructor({aa}: {\n"
                "  aa?: string,\n"
                "  aaaaaaaa?: string,\n"
@@ -1344,5 +1343,14 @@
   verifyFormat("let x = {foo: 1}!;\n");
 }
 
+TEST_F(FormatTestJS, Conditional) {
+  verifyFormat("y = x ? 1 : 2;");
+  verifyFormat("x ? 1 : 2;");
+  verifyFormat("class Foo {\n"
+               "  field = true ? 1 : 2;\n"
+               "  method(a = true ? 1 : 2) {}\n"
+               "}");
+}
+
 } // end namespace tooling
 } // end namespace clang