diff --git a/src/samples/conference/public/scripts/rest-sample.js b/src/samples/conference/public/scripts/rest-sample.js
index 5b6f05d7..03dbfe54 100644
--- a/src/samples/conference/public/scripts/rest-sample.js
+++ b/src/samples/conference/public/scripts/rest-sample.js
@@ -4,6 +4,7 @@
 
 // REST samples. It sends HTTP requests to sample server, and sample server sends requests to conference server.
 // Both this file and sample server are samples.
+'use strict';
 var send = function (method, path, body, onRes, host) {
     var req = new XMLHttpRequest()
     req.onreadystatechange = function () {
diff --git a/src/samples/p2p/js/sc.websocket.js b/src/samples/p2p/js/sc.websocket.js
index 40607ab2..1fc725da 100644
--- a/src/samples/p2p/js/sc.websocket.js
+++ b/src/samples/p2p/js/sc.websocket.js
@@ -2,6 +2,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
 /**
  * @class SignalingChannel
  * @classDesc Signaling module for Open WebRTC Toolkit P2P chat
diff --git a/src/samples/p2p/peercall.html b/src/samples/p2p/peercall.html
index fac977d5..be5176c8 100644
--- a/src/samples/p2p/peercall.html
+++ b/src/samples/p2p/peercall.html
@@ -105,6 +105,7 @@ <h2>ScreenView</h2>
   <footer id="status"></footer>
   <div id="infoDiv"></div>
   <script type="text/javascript">
+    'use strict';
     var isVideo = 1;
     var serverAddress = 'http://example.com'; // Please change example.com to signaling server's address.
     const signaling = new SignalingChannel();
diff --git a/src/sdk/base/export.js b/src/sdk/base/export.js
index 823d50bd..bbad8726 100644
--- a/src/sdk/base/export.js
+++ b/src/sdk/base/export.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 export * from './mediastream-factory.js';
 export * from './stream.js';
 export * from './mediaformat.js';
diff --git a/src/sdk/base/logger.js b/src/sdk/base/logger.js
index 16b13158..0766fc1d 100644
--- a/src/sdk/base/logger.js
+++ b/src/sdk/base/logger.js
@@ -28,12 +28,13 @@
 
 /* global console,window */
 
+'use strict';
+
 /*
  * API to write logs based on traditional logging mechanisms: debug, trace,
  * info, warning, error
  */
 const Logger = (function() {
-  'use strict';
   const DEBUG = 0;
   const TRACE = 1;
   const INFO = 2;
diff --git a/src/sdk/conference/export.js b/src/sdk/conference/export.js
index ba5dab72..1a3aee75 100644
--- a/src/sdk/conference/export.js
+++ b/src/sdk/conference/export.js
@@ -2,5 +2,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 export {ConferenceClient} from './client.js';
 export {SioSignaling} from './signaling.js';
diff --git a/src/sdk/export.js b/src/sdk/export.js
index 2639d3a7..e1974bfc 100644
--- a/src/sdk/export.js
+++ b/src/sdk/export.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 import * as base from './base/export.js';
 import * as p2p from './p2p/export.js';
 import * as conference from './conference/export.js';
diff --git a/src/sdk/p2p/error.js b/src/sdk/p2p/error.js
index 18a6efae..0db88fac 100644
--- a/src/sdk/p2p/error.js
+++ b/src/sdk/p2p/error.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 export const errors = {
   // 2100-2999 for P2P errors
   // 2100-2199 for connection errors
diff --git a/src/sdk/p2p/export.js b/src/sdk/p2p/export.js
index ca12444e..292a3162 100644
--- a/src/sdk/p2p/export.js
+++ b/src/sdk/p2p/export.js
@@ -2,5 +2,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 export {default as P2PClient} from './p2pclient.js';
 export {P2PError} from './error.js';
diff --git a/src/sdk/rest/API.js b/src/sdk/rest/API.js
index 2b872672..a7b1d39e 100644
--- a/src/sdk/rest/API.js
+++ b/src/sdk/rest/API.js
@@ -26,6 +26,8 @@
 
 // This file is borrowed from lynckia/licode with some modifications.
 
+'use strict';
+
 /*global require, CryptoJS, Buffer, url, http, https*/
 var Url = require("url");
 
diff --git a/src/sdk/rest/Base64.js b/src/sdk/rest/Base64.js
index 8c51429d..5003b412 100644
--- a/src/sdk/rest/Base64.js
+++ b/src/sdk/rest/Base64.js
@@ -26,10 +26,11 @@
 
 // This file is borrowed from lynckia/licode with some modifications.
 
+'use strict';
+
 /*global unescape*/
 var OWT_REST = OWT_REST || {};
 OWT_REST.Base64 = (function(OWT_REST) {
-  "use strict";
   var END_OF_INPUT, base64Chars, reverseBase64Chars, base64Str, base64Count,
     i, setBase64Str, readBase64, encodeBase64, readReverseBase64, ntos,
     decodeBase64;
diff --git a/src/sdk/rest/hmac-sha256.js b/src/sdk/rest/hmac-sha256.js
index a143d843..577e4eb7 100644
--- a/src/sdk/rest/hmac-sha256.js
+++ b/src/sdk/rest/hmac-sha256.js
@@ -4,6 +4,7 @@ code.google.com/p/crypto-js
 (c) 2009-2012 by Jeff Mott. All rights reserved.
 code.google.com/p/crypto-js/wiki/License
 */
+'use strict';
 var CryptoJS=CryptoJS||function(h,i){var e={},f=e.lib={},l=f.Base=function(){function a(){}return{extend:function(j){a.prototype=this;var d=new a;j&&d.mixIn(j);d.$super=this;return d},create:function(){var a=this.extend();a.init.apply(a,arguments);return a},init:function(){},mixIn:function(a){for(var d in a)a.hasOwnProperty(d)&&(this[d]=a[d]);a.hasOwnProperty("toString")&&(this.toString=a.toString)},clone:function(){return this.$super.extend(this)}}}(),k=f.WordArray=l.extend({init:function(a,j){a=
 this.words=a||[];this.sigBytes=j!=i?j:4*a.length},toString:function(a){return(a||m).stringify(this)},concat:function(a){var j=this.words,d=a.words,c=this.sigBytes,a=a.sigBytes;this.clamp();if(c%4)for(var b=0;b<a;b++)j[c+b>>>2]|=(d[b>>>2]>>>24-8*(b%4)&255)<<24-8*((c+b)%4);else if(65535<d.length)for(b=0;b<a;b+=4)j[c+b>>>2]=d[b>>>2];else j.push.apply(j,d);this.sigBytes+=a;return this},clamp:function(){var a=this.words,b=this.sigBytes;a[b>>>2]&=4294967295<<32-8*(b%4);a.length=h.ceil(b/4)},clone:function(){var a=
 l.clone.call(this);a.words=this.words.slice(0);return a},random:function(a){for(var b=[],d=0;d<a;d+=4)b.push(4294967296*h.random()|0);return k.create(b,a)}}),o=e.enc={},m=o.Hex={stringify:function(a){for(var b=a.words,a=a.sigBytes,d=[],c=0;c<a;c++){var e=b[c>>>2]>>>24-8*(c%4)&255;d.push((e>>>4).toString(16));d.push((e&15).toString(16))}return d.join("")},parse:function(a){for(var b=a.length,d=[],c=0;c<b;c+=2)d[c>>>3]|=parseInt(a.substr(c,2),16)<<24-4*(c%8);return k.create(d,b/2)}},q=o.Latin1={stringify:function(a){for(var b=
diff --git a/test/unit/resources/scripts/base.js b/test/unit/resources/scripts/base.js
index a170fd35..bfa1edb0 100644
--- a/test/unit/resources/scripts/base.js
+++ b/test/unit/resources/scripts/base.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 import * as MediaStreamFactoryModule from '../../../../src/sdk/base/mediastream-factory.js';
 import * as StreamModule from '../../../../src/sdk/base/stream.js';
 import * as MediaFormatModule from '../../../../src/sdk/base/mediaformat.js'
diff --git a/test/unit/resources/scripts/conference.js b/test/unit/resources/scripts/conference.js
index a045e619..f28e3be1 100644
--- a/test/unit/resources/scripts/conference.js
+++ b/test/unit/resources/scripts/conference.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 import {ConferenceClient} from '../../../../src/sdk/conference/client.js';
 import * as StreamModule from '../../../../src/sdk/base/stream.js';
 import * as EventModule from '../../../../src/sdk/base/event.js'
diff --git a/test/unit/resources/scripts/p2p.js b/test/unit/resources/scripts/p2p.js
index e3857094..c69405fc 100644
--- a/test/unit/resources/scripts/p2p.js
+++ b/test/unit/resources/scripts/p2p.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 import P2PClient from '../../../../src/sdk/p2p/p2pclient.js';
 import SignalingChannel from './fake-p2p-signaling.js';
 import * as StreamModule from '../../../../src/sdk/base/stream.js';
diff --git a/test/unit/resources/scripts/runner.js b/test/unit/resources/scripts/runner.js
index 948f7460..2b7da502 100644
--- a/test/unit/resources/scripts/runner.js
+++ b/test/unit/resources/scripts/runner.js
@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+'use strict';
+
 import * as base from './base.js';
 import * as p2p from './p2p.js';
 import * as conference from './conference.js'