--module option, enables strict mode and toplevel options

README.md

@@ -110,6 +110,7 @@ a double dash to prevent input files being used as option arguments:
     --keep-classnames           Do not mangle/drop class names.
     --keep-fnames               Do not mangle/drop function names.  Useful for
                                 code relying on Function.prototype.name.
+    --module                    Input is an ES6 module
     --name-cache <file>         File to hold mangled name mappings.
     --safari10                  Support non-standard Safari 10/11.
                                 Equivalent to setting `safari10: true` in `minify()`

bin/uglifyjs

@@ -44,6 +44,7 @@ program.option("--ecma <version>", "Specify ECMAScript release: 5, 6, 7 or 8.");
 program.option("--ie8", "Support non-standard Internet Explorer 8.");
 program.option("--keep-classnames", "Do not mangle/drop class names.");
 program.option("--keep-fnames", "Do not mangle/drop function names. Useful for code relying on Function.prototype.name.");
+program.option("--module", "Input is an ES6 module");
 program.option("--name-cache <file>", "File to hold mangled name mappings.");
 program.option("--rename", "Force symbol expansion.");
 program.option("--no-rename", "Disable symbol expansion.");
@@ -66,6 +67,7 @@ if (!program.output && program.sourceMap && program.sourceMap.url != "inline") {
     "compress",
     "ie8",
     "mangle",
+    "module",
     "safari10",
     "sourceMap",
     "toplevel",

lib/compress.js

@@ -73,6 +73,7 @@ function Compressor(options, false_by_default) {
         keep_fnames   : false,
         keep_infinity : false,
         loops         : !false_by_default,
+        module        : false,
         negate_iife   : !false_by_default,
         passes        : 1,
         properties    : !false_by_default,
@@ -138,6 +139,9 @@ function Compressor(options, false_by_default) {
         funcs: toplevel,
         vars: toplevel
     };
+    if (this.options['module']) {
+        this.directives['use strict'] = true;
+    }
     var sequences = this.options["sequences"];
     this.sequences_limit = sequences == 1 ? 800 : sequences | 0;
     this.warnings_produced = {};

lib/minify.js

@@ -52,6 +52,7 @@ function minify(files, options) {
             keep_classnames: undefined,
             keep_fnames: false,
             mangle: {},
+            module: false,
             nameCache: null,
             output: {},
             parse: {},
@@ -76,6 +77,7 @@ function minify(files, options) {
         set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
         set_shorthand("keep_classnames", options, [ "compress", "mangle" ]);
         set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
+        set_shorthand("module", options, [ "compress" ]);
         set_shorthand("safari10", options, [ "mangle", "output" ]);
         set_shorthand("toplevel", options, [ "compress", "mangle" ]);
         set_shorthand("warnings", options, [ "compress" ]);

test/compress/harmony.js

@@ -1601,3 +1601,19 @@ issue_2874_3: {
     ]
     node_version: ">=6"
 }
+
+module_enables_strict_mode: {
+    options = {
+        module: true,
+    }
+    input: {
+        if (1) {
+            function xyz() {}
+        }
+    }
+    expect: {
+        if (1) {
+            function xyz() {}
+        }
+    }
+}