diff --git a/index.php b/index.php
index a1bcd5643..31d767038 100644
--- a/index.php
+++ b/index.php
@@ -110,6 +110,7 @@
 	} ?>
 
 	<script type="text/javascript">
+		'use strict';
 		require({cache:{}});
 	<?php
 		require_once 'lib/jshrink/Minifier.php';
diff --git a/js/PluginHost.js b/js/PluginHost.js
index ae89ba481..88e2660ed 100644
--- a/js/PluginHost.js
+++ b/js/PluginHost.js
@@ -22,7 +22,7 @@ var PluginHost = {
 		console.warn('PluginHost::run ' + name);
 
 		if (typeof(this.hooks[name]) != 'undefined')
-			for (i = 0; i < this.hooks[name].length; i++)
+			for (var i = 0; i < this.hooks[name].length; i++)
 				if (!this.hooks[name][i](args)) break;
 	}
 };
diff --git a/js/feedlist.js b/js/feedlist.js
index 1e783f3b3..028c8737d 100644
--- a/js/feedlist.js
+++ b/js/feedlist.js
@@ -164,7 +164,7 @@ function viewfeed(params) {
 		window.open("backend.php" + query + "&debug=1&csrf_token=" + getInitParam("csrf_token"));
 	}
 
-	timeout_ms = can_wait ? 250 : 0;
+	var timeout_ms = can_wait ? 250 : 0;
 	_viewfeed_timeout = setTimeout(function() {
 
 		new Ajax.Request("backend.php", {
diff --git a/js/functions.js b/js/functions.js
index 9ae205cb3..46b9958ea 100755
--- a/js/functions.js
+++ b/js/functions.js
@@ -1117,7 +1117,7 @@ function backend_sanity_check_callback(transport) {
 	if (params) {
 		console.log('reading init-params...');
 
-		for (k in params) {
+		for (var k in params) {
 			console.log("IP: " + k + " => " + JSON.stringify(params[k]));
 			if (k == "label_base_index") _label_base_index = parseInt(params[k]);
 		}
diff --git a/js/prefs.js b/js/prefs.js
index a3f32dcbc..aa06674df 100755
--- a/js/prefs.js
+++ b/js/prefs.js
@@ -939,7 +939,7 @@ function pref_hotkey_handler(e) {
 	var hotkey_action = false;
 	var hotkeys = getInitParam("hotkeys");
 
-	for (sequence in hotkeys[1]) {
+	for (var sequence in hotkeys[1]) {
 		if (sequence == hotkey) {
 			hotkey_action = hotkeys[1][sequence];
 			break;
diff --git a/js/tt-rss.js b/js/tt-rss.js
index 4df1b04ee..d5d31cfed 100644
--- a/js/tt-rss.js
+++ b/js/tt-rss.js
@@ -628,7 +628,7 @@ function init_second_stage() {
 	var hotkeys = getInitParam("hotkeys");
 	var tmp = [];
 
-	for (sequence in hotkeys[1]) {
+	for (var sequence in hotkeys[1]) {
 		filtered = sequence.replace(/\|.*$/, "");
 		tmp[filtered] = hotkeys[1][sequence];
 	}
@@ -752,7 +752,7 @@ function parse_runtime_info(data) {
 
 	//console.log("parsing runtime info...");
 
-	for (k in data) {
+	for (var k in data) {
 		var v = data[k];
 
 //		console.log("RI: " + k + " => " + v);
@@ -899,7 +899,7 @@ function hotkey_handler(e) {
 	var hotkey_action = false;
 	var hotkeys = getInitParam("hotkeys");
 
-	for (sequence in hotkeys[1]) {
+	for (var sequence in hotkeys[1]) {
 		if (sequence == hotkey) {
 			hotkey_action = hotkeys[1][sequence];
 			break;
@@ -1076,11 +1076,11 @@ function update_random_feed() {
 }
 
 function hash_get(key) {
-	kv = window.location.hash.substring(1).toQueryParams();
+	var kv = window.location.hash.substring(1).toQueryParams();
 	return kv[key];
 }
 function hash_set(key, value) {
-	kv = window.location.hash.substring(1).toQueryParams();
+	var kv = window.location.hash.substring(1).toQueryParams();
 	kv[key] = value;
 	window.location.hash = $H(kv).toQueryString();
 }
diff --git a/js/viewfeed.js b/js/viewfeed.js
index ffd8fcf46..925d71379 100755
--- a/js/viewfeed.js
+++ b/js/viewfeed.js
@@ -470,7 +470,7 @@ function togglePub(id, client_only, no_effects, note) {
 			imgs.push(fte[i]);
 	}
 
-	for (i = 0; i < imgs.length; i++) {
+	for (var i = 0; i < imgs.length; i++) {
 		var img = imgs[i];
 
 		if (!row.hasClassName("published") || note != undefined) {