Accept object literal commas in ES3, preserve in ES5.

src/compiler/parser.ts

@@ -2106,14 +2106,20 @@ module ts {
         function parseObjectLiteral(): ObjectLiteral {
             var node = <ObjectLiteral>createNode(SyntaxKind.ObjectLiteral);
             parseExpected(SyntaxKind.OpenBraceToken);
-            if (scanner.hasPrecedingLineBreak()) node.flags |= NodeFlags.MultiLine;
-            node.properties = parseDelimitedList(ParsingContext.ObjectLiteralMembers, parseObjectLiteralMember, TrailingCommaBehavior.Allow);
+            if (scanner.hasPrecedingLineBreak()) {
+                node.flags |= NodeFlags.MultiLine;
+            }
+
+            // ES3 itself does not accept a trailing comma in an object literal, however, we'd like to preserve it in ES5.
+            var trailingCommaBehavior = languageVersion === ScriptTarget.ES3 ? TrailingCommaBehavior.Allow : TrailingCommaBehavior.Preserve;
+
+            node.properties = parseDelimitedList(ParsingContext.ObjectLiteralMembers, parseObjectLiteralMember, trailingCommaBehavior);
             parseExpected(SyntaxKind.CloseBraceToken);
 
             var seen: Map<SymbolFlags> = {};
             var Property    = 1;
             var GetAccessor = 2;
-            var SetAccesor = 4;
+            var SetAccesor =  4;
             var GetOrSetAccessor = GetAccessor | SetAccesor;
             forEach(node.properties, (p: Declaration) => {
                 if (p.kind === SyntaxKind.OmittedExpression) {

tests/baselines/reference/trailingCommasES3.js

@@ -0,0 +1,25 @@
+//// [trailingCommasES3.ts]
+
+var o1 = { a: 1, b: 2 };
+var o2 = { a: 1, b: 2, };
+var o3 = { a: 1, };
+var o4 = {};
+
+var a1 = [1, 2];
+var a2 = [1, 2, ];
+var a3 = [1, ];
+var a4 = [];
+var a5 = [1, , ];
+var a6 = [, , ];
+
+//// [trailingCommasES3.js]
+var o1 = { a: 1, b: 2 };
+var o2 = { a: 1, b: 2 };
+var o3 = { a: 1 };
+var o4 = {};
+var a1 = [1, 2];
+var a2 = [1, 2, ];
+var a3 = [1, ];
+var a4 = [];
+var a5 = [1, , ];
+var a6 = [, , ];

tests/baselines/reference/trailingCommasES5.js

@@ -0,0 +1,25 @@
+//// [trailingCommasES5.ts]
+
+var o1 = { a: 1, b: 2 };
+var o2 = { a: 1, b: 2, };
+var o3 = { a: 1, };
+var o4 = {};
+
+var a1 = [1, 2];
+var a2 = [1, 2, ];
+var a3 = [1, ];
+var a4 = [];
+var a5 = [1, , ];
+var a6 = [, , ];
+
+//// [trailingCommasES5.js]
+var o1 = { a: 1, b: 2 };
+var o2 = { a: 1, b: 2,  };
+var o3 = { a: 1,  };
+var o4 = {};
+var a1 = [1, 2];
+var a2 = [1, 2, ];
+var a3 = [1, ];
+var a4 = [];
+var a5 = [1, , ];
+var a6 = [, , ];

tests/cases/compiler/trailingCommasES3.ts

@@ -0,0 +1,13 @@
+// @target: es3
+
+var o1 = { a: 1, b: 2 };
+var o2 = { a: 1, b: 2, };
+var o3 = { a: 1, };
+var o4 = {};
+
+var a1 = [1, 2];
+var a2 = [1, 2, ];
+var a3 = [1, ];
+var a4 = [];
+var a5 = [1, , ];
+var a6 = [, , ];

tests/cases/compiler/trailingCommasES5.ts

@@ -0,0 +1,13 @@
+// @target: es5
+
+var o1 = { a: 1, b: 2 };
+var o2 = { a: 1, b: 2, };
+var o3 = { a: 1, };
+var o4 = {};
+
+var a1 = [1, 2];
+var a2 = [1, 2, ];
+var a3 = [1, ];
+var a4 = [];
+var a5 = [1, , ];
+var a6 = [, , ];