replace `(function(){ ...no side effects ... })()` with `undefined`.

1 files changed, 13 insertions, 3 deletions

diff --git a/lib/compress.js b/lib/compress.js
index fcf022e1..a4ac691a 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -673,16 +673,19 @@ merge(Compressor.prototype, {
         def(AST_EmptyStatement, function(){ return false });
         def(AST_Constant, function(){ return false });
         def(AST_This, function(){ return false });
-        def(AST_Function, function(){ return false });
-        def(AST_BlockStatement, function(){
+
+        function block(){
             for (var i = this.body.length; --i >= 0;) {
                 if (this.body[i].has_side_effects())
                     return true;
             }
             return false;
-        });
+        };
+        def(AST_Block, block);
+        def(AST_BlockStatement, block);
 
         def(AST_SimpleStatement, function(){
+            if (this.body instanceof AST_Function) return false;
             return this.body.has_side_effects();
         });
         def(AST_Binary, function(){
@@ -1281,6 +1284,13 @@ merge(Compressor.prototype, {
                 });
             }
         }
+        if (compressor.option("side_effects")) {
+            if (self.expression instanceof AST_Function
+                && self.args.length == 0
+                && !self.expression.has_side_effects()) {
+                return make_node(AST_Undefined, self);
+            }
+        }
         return self;
     });