Index: lib/Format/FormatToken.h
===================================================================
--- lib/Format/FormatToken.h
+++ lib/Format/FormatToken.h
@@ -641,6 +641,7 @@
     kw_is = &IdentTable.get("is");
     kw_let = &IdentTable.get("let");
     kw_module = &IdentTable.get("module");
+    kw_readonly = &IdentTable.get("readonly");
     kw_set = &IdentTable.get("set");
     kw_type = &IdentTable.get("type");
     kw_var = &IdentTable.get("var");
@@ -678,8 +679,8 @@
     // already initialized.
     JsExtraKeywords = std::unordered_set<IdentifierInfo *>(
         {kw_as, kw_async, kw_await, kw_declare, kw_finally, kw_from,
-         kw_function, kw_get, kw_import, kw_is, kw_let, kw_module, kw_set,
-         kw_type, kw_var, kw_yield,
+         kw_function, kw_get, kw_import, kw_is, kw_let, kw_module, kw_readonly,
+         kw_set, kw_type, kw_var, kw_yield,
          // Keywords from the Java section.
          kw_abstract, kw_extends, kw_implements, kw_instanceof, kw_interface});
   }
@@ -710,6 +711,7 @@
   IdentifierInfo *kw_is;
   IdentifierInfo *kw_let;
   IdentifierInfo *kw_module;
+  IdentifierInfo *kw_readonly;
   IdentifierInfo *kw_set;
   IdentifierInfo *kw_type;
   IdentifierInfo *kw_var;
Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -2629,11 +2629,12 @@
   } else if (Style.Language == FormatStyle::LK_JavaScript) {
     const FormatToken *NonComment = Right.getPreviousNonComment();
     if (NonComment &&
-        NonComment->isOneOf(
-            tok::kw_return, tok::kw_continue, tok::kw_break, tok::kw_throw,
-            Keywords.kw_interface, Keywords.kw_type, tok::kw_static,
-            tok::kw_public, tok::kw_private, tok::kw_protected,
-            Keywords.kw_abstract, Keywords.kw_get, Keywords.kw_set))
+        NonComment->isOneOf(tok::kw_return, tok::kw_continue, tok::kw_break,
+                            tok::kw_throw, Keywords.kw_interface,
+                            Keywords.kw_type, tok::kw_static, tok::kw_public,
+                            tok::kw_private, tok::kw_protected,
+                            Keywords.kw_readonly, Keywords.kw_abstract,
+                            Keywords.kw_get, Keywords.kw_set))
       return false; // Otherwise automatic semicolon insertion would trigger.
     if (Left.is(TT_JsFatArrow) && Right.is(tok::l_brace))
       return false;
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -930,6 +930,14 @@
                "  aaa\n"
                "];",
                getGoogleJSStyleWithColumns(12));
+  verifyFormat("class X {\n"
+               "  readonly ratherLongField =\n"
+               "      1;\n"
+               "}",
+               "class X {\n"
+               "  readonly ratherLongField = 1;\n"
+               "}",
+               getGoogleJSStyleWithColumns(12));
 }
 
 TEST_F(FormatTestJS, AutomaticSemicolonInsertionHeuristic) {