Index: cfe/trunk/lib/Format/ContinuationIndenter.cpp
===================================================================
--- cfe/trunk/lib/Format/ContinuationIndenter.cpp
+++ cfe/trunk/lib/Format/ContinuationIndenter.cpp
@@ -674,6 +674,8 @@
       return State.Stack[State.Stack.size() - 2].LastSpace;
     return State.FirstIndent;
   }
+  if (Current.is(tok::r_paren) && State.Stack.size() > 1)
+    return State.Stack[State.Stack.size() - 2].LastSpace;
   if (NextNonComment->is(TT_TemplateString) && NextNonComment->closesScope())
     return State.Stack[State.Stack.size() - 2].LastSpace;
   if (Current.is(tok::identifier) && Current.Next &&
@@ -1038,13 +1040,20 @@
       NestedBlockIndent = Column;
     }
 
+    bool EndsInComma =
+        Current.MatchingParen &&
+        Current.MatchingParen->getPreviousNonComment() &&
+        Current.MatchingParen->getPreviousNonComment()->is(tok::comma);
+
     AvoidBinPacking =
+        (Style.Language == FormatStyle::LK_JavaScript && EndsInComma) ||
         (State.Line->MustBeDeclaration && !Style.BinPackParameters) ||
         (!State.Line->MustBeDeclaration && !Style.BinPackArguments) ||
         (Style.ExperimentalAutoDetectBinPacking &&
          (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 +1074,9 @@
         }
       }
     }
+
+    if (Style.Language == FormatStyle::LK_JavaScript && 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: cfe/trunk/lib/Format/TokenAnnotator.cpp
===================================================================
--- cfe/trunk/lib/Format/TokenAnnotator.cpp
+++ cfe/trunk/lib/Format/TokenAnnotator.cpp
@@ -2463,16 +2463,20 @@
       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) ||
+       (Style.Language == FormatStyle::LK_JavaScript &&
+        Left.is(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) ||
+            (Style.Language == FormatStyle::LK_JavaScript &&
+             Right.MatchingParen->is(tok::l_paren))))
     BeforeClosingBrace = &Left;
   if (BeforeClosingBrace && (BeforeClosingBrace->is(tok::comma) ||
                              BeforeClosingBrace->isTrailingComment()))
Index: cfe/trunk/unittests/Format/FormatTest.cpp
===================================================================
--- cfe/trunk/unittests/Format/FormatTest.cpp
+++ cfe/trunk/unittests/Format/FormatTest.cpp
@@ -2106,7 +2106,7 @@
 
   verifyIncompleteFormat("void f(\n"
                          "#if A\n"
-                         "    );\n"
+                         ");\n"
                          "#else\n"
                          "#endif");
 }
@@ -4475,7 +4475,7 @@
   EXPECT_EQ("static_cast<A< //\n"
             "    B> *>(\n"
             "\n"
-            "    );",
+            ");",
             format("static_cast<A<//\n"
                    "    B>*>(\n"
                    "\n"
@@ -6567,7 +6567,7 @@
             "#if !TEST\n"
             "    _T(\"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXn\")\n"
             "#endif\n"
-            "    );",
+            ");",
             format("f(\n"
                    "#if !TEST\n"
                    "_T(\"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXn\")\n"
@@ -9639,7 +9639,7 @@
   // Other corner cases.
   verifyFormat("void f() {\n"
                "  bar([]() {} // Did not respect SpacesBeforeTrailingComments\n"
-               "      );\n"
+               "  );\n"
                "}");
 
   // Lambdas created through weird macros.
Index: cfe/trunk/unittests/Format/FormatTestJS.cpp
===================================================================
--- cfe/trunk/unittests/Format/FormatTestJS.cpp
+++ cfe/trunk/unittests/Format/FormatTestJS.cpp
@@ -550,6 +550,30 @@
                "}\n");
 }
 
+TEST_F(FormatTestJS, FunctionParametersTrailingComma) {
+  verifyFormat("function trailingComma(\n"
+               "    p1,\n"
+               "    p2,\n"
+               "    p3,\n"
+               ") {\n"
+               "  a;  //\n"
+               "}\n",
+               "function trailingComma(p1, p2, p3,) {\n"
+               "  a;  //\n"
+               "}\n");
+  verifyFormat("trailingComma(\n"
+               "    p1,\n"
+               "    p2,\n"
+               "    p3,\n"
+               ");\n",
+               "trailingComma(p1, p2, p3,);\n");
+  verifyFormat("trailingComma(\n"
+               "    p1  // hello\n"
+               ");\n",
+               "trailingComma(p1 // hello\n"
+               ");\n");
+}
+
 TEST_F(FormatTestJS, ArrayLiterals) {
   verifyFormat("var aaaaa: List<SomeThing> =\n"
                "    [new SomeThingAAAAAAAAAAAA(), new SomeThingBBBBBBBBB()];");
@@ -691,7 +715,7 @@
                "})\n"
                "    .doSomethingElse(\n"
                "        // break\n"
-               "        );");
+               "    );");
 
   Style.ColumnLimit = 33;
   verifyFormat("f({a: function() { return 1; }});", Style);
@@ -858,7 +882,7 @@
                "})\n"
                "    .doSomethingElse(\n"
                "        // break\n"
-               "        );");
+               "    );");
 }
 
 TEST_F(FormatTestJS, ReturnStatements) {