optimizations for && and || where left side is constant expression

1 files changed, 28 insertions, 0 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 530e7c2f..34233143 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2104,6 +2104,34 @@ merge(Compressor.prototype, {
             }
             break;
         }
+        if (compressor.option("conditionals")) {
+            if (self.operator == "&&") {
+                var ll = self.left.evaluate(compressor);
+                var rr = self.right.evaluate(compressor);
+                if (ll.length > 1) {
+                    if (ll[1]) {
+                        compressor.warn("Condition left of && always true [{file}:{line},{col}]", self.start);
+                        return rr[0];
+                    } else {
+                        compressor.warn("Condition left of && always false [{file}:{line},{col}]", self.start);
+                        return ll[0];
+                    }
+                }
+            }
+            if (self.operator == "||") {
+                var ll = self.left.evaluate(compressor);
+                var rr = self.right.evaluate(compressor);
+                if (ll.length > 1) {
+                    if (ll[1]) {
+                        compressor.warn("Condition left of || always true [{file}:{line},{col}]", self.start);
+                        return ll[0];
+                    } else {
+                        compressor.warn("Condition left of || always false [{file}:{line},{col}]", self.start);
+                        return rr[0];
+                    }
+                }
+            }
+        }
         if (compressor.option("booleans") && compressor.in_boolean_context()) switch (self.operator) {
           case "&&":
             var ll = self.left.evaluate(compressor);