Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -2123,6 +2123,10 @@
       // locations that should have whitespace following are identified by the
       // above set of follower tokens.
       return false;
+    // Postfix non-null assertion operator, as in `foo!.bar()`.
+    if (Right.is(tok::exclaim) && Right.Next &&
+        Right.Next->isNot(tok::identifier) && !Right.Next->Tok.isLiteral())
+      return false;
   } else if (Style.Language == FormatStyle::LK_Java) {
     if (Left.is(tok::r_square) && Right.is(tok::l_brace))
       return true;
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -1291,5 +1291,12 @@
                "var x   =  hello();");
 }
 
+TEST_F(FormatTestJS, NonNullAssertionOperator) {
+  verifyFormat("let x = foo!.bar();\n");
+  verifyFormat("let x = foo ? bar! : baz;\n");
+  verifyFormat("let x = !foo;\n");
+  verifyFormat("let x = foo!;\n");
+}
+
 } // end namespace tooling
 } // end namespace clang