diff --git a/src/groups/join.js b/src/groups/join.js
index 9fb02ec0bb..97f526e3a5 100644
--- a/src/groups/join.js
+++ b/src/groups/join.js
@@ -1,109 +1,206 @@
 'use strict';
 
-const winston = require('winston');
-
-const db = require('../database');
-const user = require('../user');
-const plugins = require('../plugins');
-const cache = require('../cache');
-
-module.exports = function (Groups) {
-	Groups.join = async function (groupNames, uid) {
-		if (!groupNames) {
-			throw new Error('[[error:invalid-data]]');
-		}
-		if (Array.isArray(groupNames) && !groupNames.length) {
-			return;
-		}
-		if (!Array.isArray(groupNames)) {
-			groupNames = [groupNames];
-		}
-
-		if (!uid) {
-			throw new Error('[[error:invalid-uid]]');
-		}
-
-		const [isMembers, exists, isAdmin] = await Promise.all([
-			Groups.isMemberOfGroups(uid, groupNames),
-			Groups.exists(groupNames),
-			user.isAdministrator(uid),
-		]);
-
-		const groupsToCreate = groupNames.filter((groupName, index) => groupName && !exists[index]);
-		const groupsToJoin = groupNames.filter((groupName, index) => !isMembers[index]);
-
-		if (!groupsToJoin.length) {
-			return;
-		}
-		await createNonExistingGroups(groupsToCreate);
-
-		const promises = [
-			db.sortedSetsAdd(groupsToJoin.map(groupName => `group:${groupName}:members`), Date.now(), uid),
-			db.incrObjectField(groupsToJoin.map(groupName => `group:${groupName}`), 'memberCount'),
-		];
-		if (isAdmin) {
-			promises.push(db.setsAdd(groupsToJoin.map(groupName => `group:${groupName}:owners`), uid));
-		}
-
-		await Promise.all(promises);
-
-		Groups.clearCache(uid, groupsToJoin);
-		cache.del(groupsToJoin.map(name => `group:${name}:members`));
-
-		const groupData = await Groups.getGroupsFields(groupsToJoin, ['name', 'hidden', 'memberCount']);
-		const visibleGroups = groupData.filter(groupData => groupData && !groupData.hidden);
-
-		if (visibleGroups.length) {
-			await db.sortedSetAdd(
-				'groups:visible:memberCount',
-				visibleGroups.map(groupData => groupData.memberCount),
-				visibleGroups.map(groupData => groupData.name)
-			);
+const __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
+	function adopt(value) { return value instanceof P ? value : new P((resolve) => { resolve(value); }); }
+	const res = new (P || (P = Promise))((resolve, reject) => {
+		function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
+		function rejected(value) { try { step(generator.throw(value)); } catch (e) { reject(e); } }
+		function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
+		step((generator = generator.apply(thisArg, _arguments || [])).next());
+	});
+	return res;
+};
+const __generator = (this && this.__generator) || function (thisArg, body) {
+	let f; let y; let t; let g;
+	let _ = { label: 0, sent: function () { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] };
+	return g = { next: verb(0), throw: verb(1), return: verb(2) }, typeof Symbol === 'function' && (g[Symbol.iterator] = function () { return this; }), g;
+	function verb(n) { return function (v) { return step([n, v]); }; }
+	function step(op) {
+		if (f) throw new TypeError('Generator is already executing.');
+		while (g && (g = 0, op[0] && (_ = 0)), _) {
+			try {
+				if (f = 1, y && (t = op[0] & 2 ? y.return : op[0] ? y.throw || ((t = y.return) && t.call(y), 0) : y.next) && !(t = t.call(y, op[1])).done) return t;
+				if (y = 0, t) op = [op[0] & 2, t.value];
+				switch (op[0]) {
+					case 0: case 1: t = op; break;
+					case 4: _.label++; return { value: op[1], done: false };
+					case 5: _.label++; y = op[1]; op = [0]; continue;
+					case 7: op = _.ops.pop(); _.trys.pop(); continue;
+					default:
+						if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
+						if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
+						if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
+						if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
+						if (t[2]) _.ops.pop();
+						_.trys.pop(); continue;
+				}
+				op = body.call(thisArg, _);
+			} catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
 		}
-
-		await setGroupTitleIfNotSet(groupsToJoin, uid);
-
-		plugins.hooks.fire('action:group.join', {
-			groupNames: groupsToJoin,
-			uid: uid,
+		if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
+	}
+};
+Object.defineProperty(exports, '__esModule', { value: true });
+exports.default = default_1;
+/* eslint-disable import/no-import-module-exports */
+const winston = require('winston');
+/* eslint-disable import/no-import-module-exports */
+const database_1 = require('../database');
+/* eslint-disable import/no-import-module-exports */
+const user_1 = require('../user');
+/* eslint-disable import/no-import-module-exports */
+const plugins_1 = require('../plugins');
+/* eslint-disable import/no-import-module-exports */
+const cache_1 = require('../cache');
+
+function default_1(Groups) {
+	Groups.join = function (groupNames, uid) {
+		return __awaiter(this, void 0, void 0, function () {
+			let _a; let isMembers; let exists; let isAdmin; let groupsToCreate; let groupsToJoin; let promises; let groupData; let
+				visibleGroups;
+			return __generator(this, (_b) => {
+				switch (_b.label) {
+					case 0:
+						if (!groupNames) {
+							throw new Error('[[error:invalid-data]]');
+						}
+						if (Array.isArray(groupNames) && !groupNames.length) {
+							return [2];
+						}
+						if (!Array.isArray(groupNames)) {
+							groupNames = [groupNames];
+						}
+						if (!uid) {
+							throw new Error('[[error:invalid-uid]]');
+						}
+						return [4 /* yield */, Promise.all([
+							Groups.isMemberOfGroups(uid, groupNames),
+							Groups.exists(groupNames),
+							user_1.default.isAdministrator(uid),
+						])];
+					case 1:
+						_a = _b.sent(), isMembers = _a[0], exists = _a[1], isAdmin = _a[2];
+						groupsToCreate = groupNames.filter((groupName, index) => groupName && !exists[index]);
+						groupsToJoin = groupNames.filter((groupName, index) => !isMembers[index]);
+						if (!groupsToJoin.length) {
+							return [2];
+						}
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						return [4 /* yield */, createNonExistingGroups(groupsToCreate)];
+					case 2:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						_b.sent();
+						promises = [
+							database_1.default.sortedSetsAdd(groupsToJoin.map(groupName => 'group:'.concat(groupName, ':members')), Date.now(), uid),
+							database_1.default.incrObjectField(groupsToJoin.map(groupName => 'group:'.concat(groupName)), 'memberCount'),
+						];
+						if (isAdmin) {
+							promises.push(database_1.default.setsAdd(groupsToJoin.map(groupName => 'group:'.concat(groupName, ':owners')), uid));
+						}
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						return [4 /* yield */, Promise.all(promises)];
+					case 3:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						_b.sent();
+						Groups.clearCache(uid, groupsToJoin);
+						cache_1.default.del(groupsToJoin.map(name => 'group:'.concat(name, ':members')));
+						return [4 /* yield */, Groups.getGroupsFields(groupsToJoin, ['name', 'hidden', 'memberCount'])];
+					case 4:
+						groupData = _b.sent();
+						visibleGroups = groupData.filter(groupData => groupData && !groupData.hidden);
+						if (!visibleGroups.length) return [3 /* break */, 6];
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						return [4 /* yield */, database_1.default.sortedSetAdd('groups:visible:memberCount', visibleGroups.map(groupData => groupData.memberCount), visibleGroups.map(groupData => groupData.name))];
+					case 5:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						_b.sent();
+						_b.label = 6;
+					case 6:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						return [4 /* yield */, setGroupTitleIfNotSet(groupsToJoin, uid)];
+					case 7:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						_b.sent();
+						plugins_1.default.hooks.fire('action:group.join', {
+							groupNames: groupsToJoin,
+							uid: uid,
+						});
+						return [2];
+				}
+			});
 		});
 	};
-
-	async function createNonExistingGroups(groupsToCreate) {
-		if (!groupsToCreate.length) {
-			return;
-		}
-
-		for (const groupName of groupsToCreate) {
-			try {
-				// eslint-disable-next-line no-await-in-loop
-				await Groups.create({
-					name: groupName,
-					hidden: 1,
-				});
-			} catch (err) {
-				if (err && err.message !== '[[error:group-already-exists]]') {
-					winston.error(`[groups.join] Could not create new hidden group (${groupName})\n${err.stack}`);
-					throw err;
+	function createNonExistingGroups(groupsToCreate) {
+		return __awaiter(this, void 0, void 0, function () {
+			let _i; let groupsToCreate_1; let groupName; let
+				err_1;
+			return __generator(this, (_a) => {
+				switch (_a.label) {
+					case 0:
+						if (!groupsToCreate.length) {
+							return [2];
+						}
+						_i = 0, groupsToCreate_1 = groupsToCreate;
+						_a.label = 1;
+					case 1:
+						if (!(_i < groupsToCreate_1.length)) return [3 /* break */, 6];
+						groupName = groupsToCreate_1[_i];
+						_a.label = 2;
+					case 2:
+						_a.trys.push([2, 4, , 5]);
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						// eslint-disable-next-line no-await-in-loop
+						return [4 /* yield */, Groups.create({
+							name: groupName,
+							hidden: 1,
+						})];
+					case 3:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						// eslint-disable-next-line no-await-in-loop
+						_a.sent();
+						return [3 /* break */, 5];
+					case 4:
+						err_1 = _a.sent();
+						if (err_1 && err_1.message !== '[[error:group-already-exists]]') {
+							winston.error('[groups.join] Could not create new hidden group ('.concat(groupName, ')\n').concat(err_1.stack));
+							throw err_1;
+						}
+						return [3 /* break */, 5];
+					case 5:
+						_i++;
+						return [3 /* break */, 1];
+					case 6: return [2];
 				}
-			}
-		}
+			});
+		});
 	}
-
-	async function setGroupTitleIfNotSet(groupNames, uid) {
-		const ignore = ['registered-users', 'verified-users', 'unverified-users', Groups.BANNED_USERS];
-		groupNames = groupNames.filter(
-			groupName => !ignore.includes(groupName) && !Groups.isPrivilegeGroup(groupName)
-		);
-		if (!groupNames.length) {
-			return;
-		}
-
-		const currentTitle = await db.getObjectField(`user:${uid}`, 'groupTitle');
-		if (currentTitle || currentTitle === '') {
-			return;
-		}
-
-		await user.setUserField(uid, 'groupTitle', JSON.stringify(groupNames));
+	function setGroupTitleIfNotSet(groupNames, uid) {
+		return __awaiter(this, void 0, void 0, function () {
+			let ignore; let
+				currentTitle;
+			return __generator(this, (_a) => {
+				switch (_a.label) {
+					case 0:
+						ignore = ['registered-users', 'verified-users', 'unverified-users', Groups.BANNED_USERS];
+						groupNames = groupNames.filter(groupName => !ignore.includes(groupName) && !Groups.isPrivilegeGroup(groupName));
+						if (!groupNames.length) {
+							return [2];
+						}
+						return [4 /* yield */, database_1.default.getObjectField('user:'.concat(uid), 'groupTitle')];
+					case 1:
+						currentTitle = _a.sent();
+						if (currentTitle || currentTitle === '') {
+							return [2];
+						}
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						return [4 /* yield */, user_1.default.setUserField(uid, 'groupTitle', JSON.stringify(groupNames))];
+					case 2:
+						// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+						_a.sent();
+						return [2];
+				}
+			});
+		});
 	}
-};
+}
+
diff --git a/src/groups/join.ts b/src/groups/join.ts
new file mode 100644
index 0000000000..55126f123b
--- /dev/null
+++ b/src/groups/join.ts
@@ -0,0 +1,116 @@
+'use strict';
+
+/* eslint-disable import/no-import-module-exports */
+import winston = require ('winston');
+/* eslint-disable import/no-import-module-exports */
+import db from '../database';
+/* eslint-disable import/no-import-module-exports */
+import user from '../user';
+/* eslint-disable import/no-import-module-exports */
+import plugins from '../plugins';
+/* eslint-disable import/no-import-module-exports */
+import cache from '../cache';
+
+export default function (Groups:any) {
+	Groups.join = async function (groupNames: String[] | String, uid: String): Promise<void> {
+		if (!groupNames) {
+			throw new Error('[[error:invalid-data]]');
+		}
+		if (Array.isArray(groupNames) && !groupNames.length) {
+			return;
+		}
+		if (!Array.isArray(groupNames)) {
+			groupNames = [groupNames];
+		}
+
+		if (!uid) {
+			throw new Error('[[error:invalid-uid]]');
+		}
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		const [isMembers, exists, isAdmin] = await Promise.all([
+			Groups.isMemberOfGroups(uid, groupNames),
+			Groups.exists(groupNames),
+			user.isAdministrator(uid),
+		]);
+
+		const groupsToCreate = groupNames.filter((groupName, index) => groupName && !exists[index]);
+		const groupsToJoin = groupNames.filter((groupName, index) => !isMembers[index]);
+
+		if (!groupsToJoin.length) {
+			return;
+		}
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		await createNonExistingGroups(groupsToCreate);
+
+		const promises = [
+			db.sortedSetsAdd(groupsToJoin.map(groupName => `group:${groupName}:members`), Date.now(), uid),
+			db.incrObjectField(groupsToJoin.map(groupName => `group:${groupName}`), 'memberCount'),
+		];
+		if (isAdmin) {
+			promises.push(db.setsAdd(groupsToJoin.map(groupName => `group:${groupName}:owners`), uid));
+		}
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		await Promise.all(promises);
+
+		Groups.clearCache(uid, groupsToJoin);
+		cache.del(groupsToJoin.map(name => `group:${name}:members`));
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		const groupData = await Groups.getGroupsFields(groupsToJoin, ['name', 'hidden', 'memberCount']);
+		const visibleGroups = groupData.filter((groupData: any) => groupData && !groupData.hidden);
+
+		if (visibleGroups.length) {
+			// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+			await db.sortedSetAdd(
+				'groups:visible:memberCount',
+				visibleGroups.map((groupData: any) => groupData.memberCount),
+				visibleGroups.map((groupData: any) => groupData.name)
+			);
+		}
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		await setGroupTitleIfNotSet(groupsToJoin, uid);
+
+		plugins.hooks.fire('action:group.join', {
+			groupNames: groupsToJoin,
+			uid: uid,
+		});
+	};
+
+	async function createNonExistingGroups(groupsToCreate: any): Promise<void> {
+		if (!groupsToCreate.length) {
+			return;
+		}
+
+		for (const groupName of groupsToCreate) {
+			try {
+				// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+				// eslint-disable-next-line no-await-in-loop
+				await Groups.create({
+					name: groupName,
+					hidden: 1,
+				});
+			} catch (err) {
+				if (err && (err as {message: String}).message !== '[[error:group-already-exists]]') {
+					winston.error(`[groups.join] Could not create new hidden group (${groupName})\n${(err as {stack:String}).stack}`);
+					throw err;
+				}
+			}
+		}
+	}
+
+	async function setGroupTitleIfNotSet(groupNames: String [], uid: String): Promise<void> {
+		const ignore = ['registered-users', 'verified-users', 'unverified-users', Groups.BANNED_USERS];
+		groupNames = groupNames.filter(
+			groupName => !ignore.includes(groupName) && !Groups.isPrivilegeGroup(groupName)
+		);
+		if (!groupNames.length) {
+			return;
+		}
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		const currentTitle = await db.getObjectField(`user:${uid}`, 'groupTitle');
+		if (currentTitle || currentTitle === '') {
+			return;
+		}
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
+		await user.setUserField(uid, 'groupTitle', JSON.stringify(groupNames));
+	}
+};
\ No newline at end of file
diff --git a/tsconfig.json b/tsconfig.json
index 10aeeef7e6..76c1287b0a 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     "allowJs": false,
-    "target": "es6",
+    "target": "es2017",
     "module": "commonjs",
     "moduleResolution": "node",
     "esModuleInterop": true,
@@ -14,4 +14,4 @@
   "exclude":[
     "node_modules",
   ]
-}
\ No newline at end of file
+}