optimize `return undefined` and `return void 0`

2 files changed, 239 insertions, 0 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 216aade9..ebe7e957 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -65,6 +65,7 @@ function Compressor(options, false_by_default) {
         keep_fnames   : false,
         hoist_vars    : false,
         if_return     : !false_by_default,
+        return_void_0 : !false_by_default,
         join_vars     : !false_by_default,
         cascade       : !false_by_default,
         side_effects  : !false_by_default,
@@ -2519,4 +2520,13 @@ merge(Compressor.prototype, {
     OPT(AST_Object, literals_in_boolean_context);
     OPT(AST_RegExp, literals_in_boolean_context);
 
+    OPT(AST_Return, function(self, compressor){
+        if (compressor.option("return_void_0")) {
+            if (self.value instanceof AST_Undefined) {
+                self.value = null;
+            }
+        }
+        return self;
+    });
+
 })();
diff --git a/test/compress/return_undefined.js b/test/compress/return_undefined.js
new file mode 100644
index 00000000..be79d89d
--- /dev/null
+++ b/test/compress/return_undefined.js
@@ -0,0 +1,229 @@
+return_void_0_true: {
+    options = {
+        return_void_0 : true,
+        sequences     : false,
+        if_return     : true,
+        evaluate      : true,
+        dead_code     : true,
+        conditionals  : true,
+        comparisons   : true,
+        booleans      : true,
+        unused        : true,
+        side_effects  : true,
+        properties    : true,
+        drop_debugger : true,
+        loops         : true,
+        hoist_funs    : true,
+        keep_fargs    : true,
+        keep_fnames   : false,
+        hoist_vars    : true,
+        join_vars     : true,
+        cascade       : true,
+        negate_iife   : true
+    };
+    input: {
+        function f0() {
+        }
+        function f1() {
+            return undefined;
+        }
+        function f2() {
+            return void 0;
+        }
+        function f3() {
+            return void 123;
+        }
+        function f4() {
+            return;
+        }
+        function f5(a, b) {
+            console.log(a, b);
+            baz(a);
+            return;
+        }
+        function f6(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return a + b;
+            }
+            return undefined;
+        }
+        function f7(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return void 0;
+            }
+            return a + b;
+        }
+        function f8(a, b) {
+            foo(a);
+            bar(b);
+            return void 0;
+        }
+        function f9(a, b) {
+            foo(a);
+            bar(b);
+            return undefined;
+        }
+    }
+    expect: {
+        function f0() {}
+        function f1() {}
+        function f2() {}
+        function f3() {}
+        function f4() {}
+        function f5(a, b) {
+            console.log(a, b);
+            baz(a);
+        }
+        function f6(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return a + b;
+            }
+        }
+        function f7(a, b) {
+            console.log(a, b);
+            if (!a)
+                return a + b;
+            foo(b);
+            baz(a);
+        }
+        function f8(a, b) {
+            foo(a);
+            bar(b);
+        }
+        function f9(a, b) {
+            foo(a);
+            bar(b);
+        }
+    }
+}
+
+return_void_0_false: {
+    options = {
+        return_void_0 : false,
+        sequences     : false,
+        if_return     : true,
+        evaluate      : true,
+        dead_code     : true,
+        conditionals  : true,
+        comparisons   : true,
+        booleans      : true,
+        unused        : true,
+        side_effects  : true,
+        properties    : true,
+        drop_debugger : true,
+        loops         : true,
+        hoist_funs    : true,
+        keep_fargs    : true,
+        keep_fnames   : false,
+        hoist_vars    : true,
+        join_vars     : true,
+        cascade       : true,
+        negate_iife   : true
+    };
+    input: {
+        function f0() {
+        }
+        function f1() {
+            return undefined;
+        }
+        function f2() {
+            return void 0;
+        }
+        function f3() {
+            return void 123;
+        }
+        function f4() {
+            return;
+        }
+        function f5(a, b) {
+            console.log(a, b);
+            baz(a);
+            return;
+        }
+        function f6(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return a + b;
+            }
+            return undefined;
+        }
+        function f7(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return void 0;
+            }
+            return a + b;
+        }
+        function f8(a, b) {
+            foo(a);
+            bar(b);
+            return void 0;
+        }
+        function f9(a, b) {
+            foo(a);
+            bar(b);
+            return undefined;
+        }
+    }
+    expect: {
+        function f0() {
+        }
+        function f1() {
+            return void 0;
+        }
+        function f2() {
+            return void 0;
+        }
+        function f3() {
+            return void 0;
+        }
+        function f4() {
+        }
+        function f5(a, b) {
+            console.log(a, b);
+            baz(a);
+        }
+        function f6(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return a + b;
+            }
+            return void 0;
+        }
+        function f7(a, b) {
+            console.log(a, b);
+            if (a) {
+                foo(b);
+                baz(a);
+                return void 0;
+            }
+            return a + b;
+        }
+        function f8(a, b) {
+            foo(a);
+            bar(b);
+            return void 0;
+        }
+        function f9(a, b) {
+            foo(a);
+            bar(b);
+            return void 0;
+        }
+    }
+}
+