compress object literals (#3546)

lib/compress.js

@@ -74,6 +74,7 @@ function Compressor(options, false_by_default) {
         keep_infinity   : false,
         loops           : !false_by_default,
         negate_iife     : !false_by_default,
+        objects         : !false_by_default,
         passes          : 1,
         properties      : !false_by_default,
         pure_getters    : !false_by_default && "strict",
@@ -6981,6 +6982,41 @@ merge(Compressor.prototype, {
         return self;
     });
 
+    OPT(AST_Object, function(self, compressor) {
+        if (!compressor.option("objects") || compressor.has_directive("use strict")) return self;
+        var props = self.properties;
+        var keys = new Dictionary();
+        var values = [];
+        self.properties.forEach(function(prop) {
+            if (typeof prop.key != "string") {
+                flush();
+                values.push(prop);
+                return;
+            }
+            if (prop.value.has_side_effects(compressor)) {
+                flush();
+            }
+            keys.add(prop.key, prop.value);
+        });
+        flush();
+        if (self.properties.length != values.length) {
+            return make_node(AST_Object, self, {
+                properties: values
+            });
+        }
+        return self;
+
+        function flush() {
+            keys.each(function(expressions, key) {
+                values.push(make_node(AST_ObjectKeyVal, self, {
+                    key: key,
+                    value: make_sequence(self, expressions)
+                }));
+            });
+            keys = new Dictionary();
+        }
+    });
+
     OPT(AST_Return, function(self, compressor) {
         if (self.value && is_undefined(self.value, compressor)) {
             self.value = null;