Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -2347,6 +2347,11 @@
     if (Right.is(tok::l_paren) && Line.MustBeDeclaration &&
         Left.Tok.getIdentifierInfo())
       return false;
+    // Valid JS method names can include keywords, e.g. `foo.delete()` or
+    // `bar.instanceof()`.
+    if (Right.is(tok::l_paren) && Left.Tok.getIdentifierInfo() &&
+        Left.Previous && Left.Previous->is(tok::period))
+      return false;
     if ((Left.isOneOf(Keywords.kw_let, Keywords.kw_var, Keywords.kw_in,
                       tok::kw_const) ||
          // "of" is only a keyword if it appears after another identifier
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -232,6 +232,7 @@
   verifyFormat("x.var() = 1;");
   verifyFormat("x.for() = 1;");
   verifyFormat("x.as() = 1;");
+  verifyFormat("x.instanceof() = 1;");
   verifyFormat("x = {\n"
                "  a: 12,\n"
                "  interface: 1,\n"