avoid duplicate property names in object literals under "use strict" (#2818)

fixes #2816

1 files changed, 9 insertions, 3 deletions

diff --git a/lib/compress.js b/lib/compress.js
index bda5d7a6..00593e81 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -893,7 +893,7 @@ merge(Compressor.prototype, {
                 sequencesize_2(statements, compressor);
             }
             if (compressor.option("join_vars")) {
-                join_consecutive_vars(statements, compressor);
+                join_consecutive_vars(statements);
             }
             if (compressor.option("collapse_vars")) {
                 collapse(statements, compressor);
@@ -1746,8 +1746,14 @@ merge(Compressor.prototype, {
                     prop = prop.evaluate(compressor);
                 }
                 if (prop instanceof AST_Node) break;
+                prop = "" + prop;
+                if (compressor.has_directive("use strict")) {
+                    if (!all(def.value.properties, function(node) {
+                        return node.key != prop && node.key.name != prop;
+                    })) break;
+                }
                 def.value.properties.push(make_node(AST_ObjectKeyVal, node, {
-                    key: "" + prop,
+                    key: prop,
                     value: node.right
                 }));
                 exprs.shift();
@@ -1756,7 +1762,7 @@ merge(Compressor.prototype, {
             return trimmed && exprs;
         }
 
-        function join_consecutive_vars(statements, compressor) {
+        function join_consecutive_vars(statements) {
             var defs;
             for (var i = 0, j = -1, len = statements.length; i < len; i++) {
                 var stat = statements[i];