Enable strict mode in js

This will make some types of bugs easier to detect
and supposedly some js engines can take advantage of
more optimised paths with strict mode enabled improving
performance.
Some very crude test show no significant differnce
exceeding run-to-run variance.

Author: TheOneric

Makefile

@@ -4,7 +4,7 @@
 BASE_DIR:=$(dir $(realpath $(firstword $(MAKEFILE_LIST))))
 DIST_DIR:=$(BASE_DIR)dist/libraries
 
-export LDFLAGS = -s ENVIRONMENT=web,webview,worker -s NO_EXIT_RUNTIME=1
+export LDFLAGS = -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 {