Index: lib/Format/ContinuationIndenter.cpp
===================================================================
--- lib/Format/ContinuationIndenter.cpp
+++ lib/Format/ContinuationIndenter.cpp
@@ -1045,6 +1045,7 @@
          (Current.PackingKind == PPK_OnePerLine ||
           (!BinPackInconclusiveFunctions &&
            Current.PackingKind == PPK_Inconclusive)));
+
     if (Current.is(TT_ObjCMethodExpr) && Current.MatchingParen) {
       if (Style.ColumnLimit) {
         // If this '[' opens an ObjC call, determine whether all parameters fit
@@ -1065,6 +1066,12 @@
         }
       }
     }
+
+    bool EndsInComma =
+        Current.MatchingParen &&
+        Current.MatchingParen->getPreviousNonComment() &&
+        Current.MatchingParen->getPreviousNonComment()->is(tok::comma);
+    if (EndsInComma) BreakBeforeParameter = true;
   }
   // Generally inherit NoLineBreak from the current scope to nested scope.
   // However, don't do this for non-empty nested blocks, dict literals and
Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -2463,16 +2463,16 @@
       return true;
   }
 
-  // If the last token before a '}' is a comma or a trailing comment, the
-  // intention is to insert a line break after it in order to make shuffling
-  // around entries easier.
+  // If the last token before a '}', ']', or ')' is a comma or a trailing
+  // comment, the intention is to insert a line break after it in order to make
+  // shuffling around entries easier.
   const FormatToken *BeforeClosingBrace = nullptr;
-  if (Left.isOneOf(tok::l_brace, TT_ArrayInitializerLSquare) &&
+  if (Left.isOneOf(tok::l_brace, TT_ArrayInitializerLSquare, tok::l_paren) &&
       Left.BlockKind != BK_Block && Left.MatchingParen)
     BeforeClosingBrace = Left.MatchingParen->Previous;
   else if (Right.MatchingParen &&
-           Right.MatchingParen->isOneOf(tok::l_brace,
-                                        TT_ArrayInitializerLSquare))
+           Right.MatchingParen->isOneOf(
+               tok::l_brace, TT_ArrayInitializerLSquare, tok::l_paren))
     BeforeClosingBrace = &Left;
   if (BeforeClosingBrace && (BeforeClosingBrace->is(tok::comma) ||
                              BeforeClosingBrace->isTrailingComment()))
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -550,6 +550,18 @@
                "}\n");
 }
 
+TEST_F(FormatTestJS, FunctionParametersTrailingComma) {
+  verifyFormat("function trailingComma(\n"
+               "    parameter1,\n"
+               "    parameter2,\n"
+               ") {\n"
+               "  a;  //\n"
+               "}\n",
+               "function trailingComma(parameter1, parameter2,) {\n"
+               "  a;  //\n"
+               "}\n");
+}
+
 TEST_F(FormatTestJS, ArrayLiterals) {
   verifyFormat("var aaaaa: List<SomeThing> =\n"
                "    [new SomeThingAAAAAAAAAAAA(), new SomeThingBBBBBBBBB()];");