Enable strict mode in js

This will make some types of bugs easier to detect
and avoid accidental additions of code not working
inside Modules, which always use strict mode.

Performance measurements show no relevant performance
difference between strict and non-strict mode, so this
won't cause regressions in this regard.

Author: TheOneric

Makefile

@@ -4,7 +4,7 @@
 BASE_DIR:=$(dir $(realpath $(firstword $(MAKEFILE_LIST))))
 DIST_DIR:=$(BASE_DIR)dist/libraries
 
-export LDFLAGS = -O3 -s ENVIRONMENT=web,webview,worker -s NO_EXIT_RUNTIME=1
+export LDFLAGS = -O3 -s ENVIRONMENT=web,webview,worker -s NO_EXIT_RUNTIME=1 -s STRICT_JS=1
 export CFLAGS = -O3 -s USE_PTHREADS=0
 export CXXFLAGS = $(CFLAGS)
 export PKG_CONFIG_PATH = $(DIST_DIR)/lib/pkgconfig

src/subtitles-octopus.js

@@ -1,3 +1,4 @@
+"use strict";
 var SubtitlesOctopus = function (options) {
     var supportsWebAssembly = false;
     try {