diff --git a/dev/Common/Globals.js b/dev/Common/Globals.js
index b46eb431b..4f4ff384e 100644
--- a/dev/Common/Globals.js
+++ b/dev/Common/Globals.js
@@ -49,17 +49,17 @@ export const sUserAgent =
 /**
  * @type {boolean}
  */
-export const bIE = -1 < sUserAgent.indexOf('msie');
+export const bIE = sUserAgent.includes('msie');
 
 /**
  * @type {boolean}
  */
-export const bChrome = -1 < sUserAgent.indexOf('chrome');
+export const bChrome = sUserAgent.includes('chrome');
 
 /**
  * @type {boolean}
  */
-export const bSafari = !bChrome && -1 < sUserAgent.indexOf('safari');
+export const bSafari = !bChrome && sUserAgent.includes('safari');
 
 /**
  * @type {boolean}
diff --git a/dev/External/ko.js b/dev/External/ko.js
index 8f365c7a8..c5612a33d 100644
--- a/dev/External/ko.js
+++ b/dev/External/ko.js
@@ -818,7 +818,7 @@ ko.bindingHandlers.emailsTags = {
 			autoCompleteSource: fAutoCompleteSource,
 			splitHook: (value) => {
 				const v = Utils.trim(value);
-				if (v && -1 < inputDelimiters.indexOf(v.substr(-1))) {
+				if (v && inputDelimiters.includes(v.substr(-1))) {
 					return EmailModel.splitEmailLine(value);
 				}
 				return null;
diff --git a/dev/Model/Email.js b/dev/Model/Email.js
index 274bebc41..2bfa212d9 100644
--- a/dev/Model/Email.js
+++ b/dev/Model/Email.js
@@ -73,7 +73,7 @@ class EmailModel {
 	 * @returns {boolean}
 	 */
 	search(query) {
-		return -1 < (this.name + ' ' + this.email).toLowerCase().indexOf(query.toLowerCase());
+		return (this.name + ' ' + this.email).toLowerCase().includes(query.toLowerCase());
 	}
 
 	/**
diff --git a/dev/Promises/User/Populator.js b/dev/Promises/User/Populator.js
index 8602ab670..34c09b1de 100644
--- a/dev/Promises/User/Populator.js
+++ b/dev/Promises/User/Populator.js
@@ -23,7 +23,7 @@ class PromisesUserPopulator extends AbstractBasicPromises {
 	 * @returns {boolean}
 	 */
 	isFolderExpanded(sFullNameHash, expandedFolders) {
-		return expandedFolders && isArray(expandedFolders) && -1 !== _.indexOf(expandedFolders, sFullNameHash);
+		return expandedFolders && isArray(expandedFolders) && expandedFolders.includes(sFullNameHash);
 	}
 
 	/**
diff --git a/dev/Remote/User/Ajax.js b/dev/Remote/User/Ajax.js
index 59ffdea93..8fc5cfe08 100644
--- a/dev/Remote/User/Ajax.js
+++ b/dev/Remote/User/Ajax.js
@@ -315,7 +315,7 @@ class RemoteUserAjax extends AbstractAjaxRemote {
 			useThreads = AppStore.threadsAllowed() && SettingsStore.useThreads(),
 			inboxUidNext = getFolderInboxName() === sFolderFullNameRaw ? getFolderUidNext(sFolderFullNameRaw) : '';
 
-		if ('' !== folderHash && ('' === sSearch || -1 === sSearch.indexOf('is:'))) {
+		if ('' !== folderHash && ('' === sSearch || !sSearch.includes('is:'))) {
 			return this.defaultRequest(
 				fCallback,
 				'MessageList',
diff --git a/dev/Stores/User/Pgp.js b/dev/Stores/User/Pgp.js
index 34d8951de..befa7b877 100644
--- a/dev/Stores/User/Pgp.js
+++ b/dev/Stores/User/Pgp.js
@@ -30,7 +30,7 @@ class PgpUserStore {
 	}
 
 	findKeyByHex(keys, hash) {
-		return _.find(keys, (item) => hash && item && (hash === item.id || -1 < item.ids.indexOf(hash)));
+		return _.find(keys, (item) => hash && item && (hash === item.id || item.ids.includes(hash)));
 	}
 
 	findPublicKeyByHex(hash) {
@@ -45,7 +45,7 @@ class PgpUserStore {
 		return _.compact(
 			_.flatten(
 				_.map(this.openpgpkeysPublic(), (item) => {
-					const key = item && -1 < item.emails.indexOf(email) ? item : null;
+					const key = item && item.emails.includes(email) ? item : null;
 					return key ? key.getNativeKeys() : [null];
 				}),
 				true
@@ -108,7 +108,7 @@ class PgpUserStore {
 	 * @returns {?}
 	 */
 	findPublicKeyByEmailNotNative(email) {
-		return _.find(this.openpgpkeysPublic(), (item) => item && -1 < item.emails.indexOf(email)) || null;
+		return _.find(this.openpgpkeysPublic(), (item) => item && item.emails.includes(email)) || null;
 	}
 
 	/**
@@ -116,7 +116,7 @@ class PgpUserStore {
 	 * @returns {?}
 	 */
 	findPrivateKeyByEmailNotNative(email) {
-		return _.find(this.openpgpkeysPrivate(), (item) => item && -1 < item.emails.indexOf(email)) || null;
+		return _.find(this.openpgpkeysPrivate(), (item) => item && item.emails.includes(email)) || null;
 	}
 
 	/**
@@ -124,7 +124,7 @@ class PgpUserStore {
 	 * @returns {?}
 	 */
 	findAllPublicKeysByEmailNotNative(email) {
-		return this.openpgpkeysPublic().filter(item => item && -1 < item.emails.indexOf(email)) || null;
+		return this.openpgpkeysPublic().filter(item => item && item.emails.includes(email)) || null;
 	}
 
 	/**
@@ -132,7 +132,7 @@ class PgpUserStore {
 	 * @returns {?}
 	 */
 	findAllPrivateKeysByEmailNotNative(email) {
-		return this.openpgpkeysPrivate().filter(item => item && -1 < item.emails.indexOf(email)) || null;
+		return this.openpgpkeysPrivate().filter(item => item && item.emails.includes(email)) || null;
 	}
 
 	/**
@@ -142,7 +142,7 @@ class PgpUserStore {
 	 */
 	findPrivateKeyByEmail(email, password) {
 		let privateKey = null;
-		const key = _.find(this.openpgpkeysPrivate(), (item) => item && -1 < item.emails.indexOf(email));
+		const key = _.find(this.openpgpkeysPrivate(), (item) => item && item.emails.includes(email));
 
 		if (key) {
 			try {
diff --git a/dev/View/Popup/AdvancedSearch.js b/dev/View/Popup/AdvancedSearch.js
index 08aed0eba..952bd7220 100644
--- a/dev/View/Popup/AdvancedSearch.js
+++ b/dev/View/Popup/AdvancedSearch.js
@@ -73,7 +73,7 @@ class AdvancedSearchPopupView extends AbstractViewNext {
 	}
 
 	buildSearchStringValue(value) {
-		if (-1 < value.indexOf(' ')) {
+		if (value.includes(' ')) {
 			value = '"' + value + '"';
 		}
 		return value;
diff --git a/dev/View/Popup/Compose.js b/dev/View/Popup/Compose.js
index 4724e88f4..f00103867 100644
--- a/dev/View/Popup/Compose.js
+++ b/dev/View/Popup/Compose.js
@@ -739,7 +739,7 @@ class ComposePopupView extends AbstractViewNext {
 		if ('' !== fromLine) {
 			signature = signature.replace(/{{FROM-FULL}}/g, fromLine);
 
-			if (-1 === fromLine.indexOf(' ') && 0 < fromLine.indexOf('@')) {
+			if (!fromLine.includes(' ') && 0 < fromLine.indexOf('@')) {
 				fromLine = fromLine.replace(/@[\S]+/, '');
 			}
 
@@ -752,14 +752,14 @@ class ComposePopupView extends AbstractViewNext {
 		signature = signature.replace(/{{FROM}}/g, '');
 		signature = signature.replace(/{{FROM-FULL}}/g, '');
 
-		if (-1 < signature.indexOf('{{DATE}}')) {
+		if (signature.includes('{{DATE}}')) {
 			signature = signature.replace(/{{DATE}}/g, momentorFormat(0, 'llll'));
 		}
 
-		if (-1 < signature.indexOf('{{TIME}}')) {
+		if (signature.includes('{{TIME}}')) {
 			signature = signature.replace(/{{TIME}}/g, momentorFormat(0, 'LT'));
 		}
-		if (-1 < signature.indexOf('{{MOMENT:')) {
+		if (signature.includes('{{MOMENT:')) {
 			try {
 				let match = null;
 				while (null !== (match = momentRegx.exec(signature))) {