From 76df77c08c684bc49bebb35d6d527d90cea48108 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Thu, 28 Jun 2018 18:16:49 +0800
Subject: implement `directives` (#3203)

fixes #3166
---
 lib/compress.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

(limited to 'lib')

diff --git a/lib/compress.js b/lib/compress.js
index e347169e..70ee9363 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -54,6 +54,7 @@ function Compressor(options, false_by_default) {
         comparisons   : !false_by_default,
         conditionals  : !false_by_default,
         dead_code     : !false_by_default,
+        directives    : !false_by_default,
         drop_console  : false,
         drop_debugger : !false_by_default,
         evaluate      : !false_by_default,
@@ -3264,8 +3265,10 @@ merge(Compressor.prototype, {
 
     /* -----[ optimizers ]----- */
 
+    var directives = makePredicate(["use asm", "use strict"]);
     OPT(AST_Directive, function(self, compressor) {
-        if (compressor.has_directive(self.value) !== self) {
+        if (compressor.option("directives")
+            && (!directives[self.value] || compressor.has_directive(self.value) !== self)) {
             return make_node(AST_EmptyStatement, self);
         }
         return self;
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