diff --git a/package-lock.json b/package-lock.json
index d775457..551a4d4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,5 +1,5 @@
 {
-  "name": "template-nodejs-elasticsearch-microservice",
+  "name": "x5gon-elasticsearch-microservice",
   "version": "1.0.0",
   "lockfileVersion": 1,
   "requires": true,
@@ -138,15 +138,6 @@
         "@types/range-parser": "*"
       }
     },
-    "@types/express-validator": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/@types/express-validator/-/express-validator-3.0.0.tgz",
-      "integrity": "sha512-LusnB0YhTXpBT25PXyGPQlK7leE1e41Vezq1hHEUwjfkopM1Pkv2X2Ppxqh9c+w/HZ6Udzki8AJotKNjDTGdkQ==",
-      "dev": true,
-      "requires": {
-        "express-validator": "*"
-      }
-    },
     "@types/express-winston": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/@types/express-winston/-/express-winston-4.0.0.tgz",
diff --git a/package.json b/package.json
index 4548134..d116cd8 100644
--- a/package.json
+++ b/package.json
@@ -51,7 +51,6 @@
     "@types/cookie-parser": "^1.4.2",
     "@types/elasticsearch": "^5.0.36",
     "@types/express": "^4.17.3",
-    "@types/express-validator": "^3.0.0",
     "@types/express-winston": "^4.0.0",
     "@types/node": "^13.9.2",
     "mocha": "^7.1.1",
diff --git a/src/Interfaces.ts b/src/Interfaces.ts
index d0a9767..fbffb25 100644
--- a/src/Interfaces.ts
+++ b/src/Interfaces.ts
@@ -20,4 +20,70 @@ export interface IConfiguration {
     elasticsearch: {
         node: string
     }
+}
+
+////////////////////////////////////////////////////////////////////////
+// Elasticsearch records
+
+export interface IContent {
+    content_id: number
+}
+
+export interface IWikipedia {
+    uri: string,
+    name: string,
+    sec_uri: string,
+    sec_name: string
+}
+
+export interface IElasticsearchHit {
+    _score: number,
+    _source: {
+        material_id: number,
+        title: string,
+        description: string,
+        creation_date: string,
+        retrieved_date: string,
+        type: string,
+        mimetype: string,
+        material_url: string,
+        website_url: string,
+        language: string,
+        license: {
+            short_name: string,
+            typed_name?: string[],
+            disclaimer: string,
+            url: string
+        },
+        contents?: IContent[],
+        provider_id: number,
+        provider_name: string,
+        provider_url: string,
+        wikipedia: IWikipedia[]
+    }
+}
+
+
+////////////////////////////////////////////////////////////////////////
+// Express API routes
+
+export interface ISearch {
+    text?: string,
+    url?: string,
+    types?: string,
+    licenses?: string,
+    languages?: string,
+    content_languages?: string,
+    provider_ids?: string,
+    wikipedia?: boolean,
+    wikipedia_limit?: number,
+    limit?: number,
+    page?: number
+}
+
+export interface IQueryElement {
+    term?: object,
+    terms?: object,
+    regexp?: object,
+    exists?: object
 }
\ No newline at end of file
diff --git a/src/load/create-elasticsearch-index.js b/src/load/create-elasticsearch-index.js
index 23ef649..10722ec 100644
--- a/src/load/create-elasticsearch-index.js
+++ b/src/load/create-elasticsearch-index.js
@@ -28,7 +28,7 @@ function materialType(mimetype) {
 }
 
 // merges all of the material information into a single line
-const pg_command = `
+const pgCommand = `
     WITH URLS AS (
         SELECT
             COALESCE(m.material_id, c.material_id) AS material_id,
@@ -162,7 +162,7 @@ async function populate() {
 
         console.log("executing pg-command");
 
-        pg.executeLarge(pg_command, [], 100,
+        pg.executeLarge(pgCommand, [], 100,
             (error, records, callback) => {
                 if (error) { console.log(error); return; }
 
@@ -179,26 +179,26 @@ async function populate() {
 
                     // modify the license attribute when sending to elasticsearch
                     const url = record.license;
-                    let short_name;
-                    let typed_name;
+                    let shortName;
+                    let typedName;
                     let disclaimer = DEFAULT_DISCLAIMER;
 
                     if (url) {
                         const regex = /\/licen[sc]es\/([\w\-]+)\//;
-                        short_name = url.match(regex)[1];
-                        typed_name = short_name.split("-");
+                        shortName = url.match(regex)[1];
+                        typedName = shortName.split("-");
                     } else {
-                        short_name = NO_LICENSE_DISCLAIMER;
+                        shortName = NO_LICENSE_DISCLAIMER;
                     }
                     record.license = {
-                        short_name,
-                        typed_name,
+                        short_name: shortName,
+                        typed_name: typedName,
                         disclaimer,
                         url
                     };
 
                     // modify the wikipedia array
-                    for (let value of record.wikipedia) {
+                    for (const value of record.wikipedia) {
                         // rename the wikipedia concepts
                         value.sec_uri = value.secUri;
                         value.sec_name = value.secName;
@@ -221,7 +221,7 @@ async function populate() {
                                 count++;
                                 xcallback(null);
                             })
-                            .catch((error) => xcallback);
+                            .catch(xcallback);
                     });
                 }
 
diff --git a/src/routes/v1/index.ts b/src/routes/v1/index.ts
index b2297fa..d91ab76 100644
--- a/src/routes/v1/index.ts
+++ b/src/routes/v1/index.ts
@@ -1,9 +1,12 @@
 import { Express } from "express";
 import { IConfiguration } from "../../Interfaces";
 
+import search from "./oer_materials";
+import recommend from "./recommend";
+
 // join all routers in a single function
 export default function index(app: Express, config: IConfiguration) {
     // setup the microservices API routes
-    app.use("/api/v1", require("./oer_materials")(config));
-    app.use("/api/v1", require("./recommend")(config));
+    app.use("/api/v1", search(config));
+    app.use("/api/v1", recommend(config));
 };
diff --git a/src/routes/v1/oer_materials.js b/src/routes/v1/oer_materials.ts
similarity index 76%
rename from src/routes/v1/oer_materials.js
rename to src/routes/v1/oer_materials.ts
index 1faafb7..a4bae9c 100644
--- a/src/routes/v1/oer_materials.js
+++ b/src/routes/v1/oer_materials.ts
@@ -4,26 +4,27 @@
  * manipuating data from Elastic Search.
  */
 
-const router = require("express").Router();
-const { default: Elasticsearch } = require("../../library/elasticsearch");
-const { ErrorHandler } = require("../../library/error");
+import { IConfiguration, IElasticsearchHit, ISearch, IQueryElement } from "../../Interfaces";
 
-// internal modules
-const mimetypes = require("../../config/mimetypes");
 
+import { Router, Request, Response, NextFunction } from "express";
 // validating the query parameters
-const { query, body, param } = require("express-validator");
-
+import { query, param } from "express-validator";
 // creation of the query string to help the user navigate through
-const querystring = require("querystring");
-
-/**
- * Returns the general material type.
- * @param {String} mimetype - The document mimetype.
- * @returns {String|Null} The material type.
- */
-function materialType(mimetype) {
-    for (let type in mimetypes) {
+import * as querystring from "querystring";
+// add error handling functionality
+import { ErrorHandler } from "../../library/error";
+// import elasticsearch module
+import Elasticsearch from "../../library/elasticsearch";
+// import file mimetypes lists
+import * as mimetypes from "../../config/mimetypes.json";
+
+// initialize the express router
+const router = Router();
+
+// returns the general material type
+function materialType(mimetype: string) {
+    for (const type in mimetypes) {
         if (mimetypes[type].includes(mimetype)) {
             return type;
         }
@@ -31,7 +32,8 @@ function materialType(mimetype) {
     return null;
 }
 
-function materialFormat(hit, { wikipedia, wikipedia_limit }) {
+// format the material
+function materialFormat(hit: IElasticsearchHit, wikipedia?: boolean, wikipedia_limit?: number) {
     return {
         weight: hit._score,
         material_id: hit._source.material_id,
@@ -48,9 +50,9 @@ function materialFormat(hit, { wikipedia, wikipedia_limit }) {
         provider: {
             id: hit._source.provider_id,
             name: hit._source.provider_name.toLowerCase(),
-            domain: hit._source.provider_url,
+            domain: hit._source.provider_url
         },
-        content_ids: hit._source.contents ? hit._source.contents.map((content) => content.content_id) : [],
+        content_ids: hit._source.contents ? hit._source.contents.map(content => content.content_id) : [],
         ...wikipedia && {
             wikipedia: wikipedia_limit && wikipedia_limit > 0
                 ? hit._source.wikipedia.slice(0, wikipedia_limit)
@@ -59,12 +61,8 @@ function materialFormat(hit, { wikipedia, wikipedia_limit }) {
     };
 }
 
-/**
- * @description Assign the elasticsearch API routes.
- * @param {Object} config - The configuration object.
- * @returns {Object} The search router.
- */
-module.exports = (config) => {
+// assign the elasticsearch API routes
+export default (config: IConfiguration) => {
     // set the default parameters
     const DEFAULT_LIMIT = 20;
     const MAX_LIMIT = 100;
@@ -85,40 +83,39 @@ module.exports = (config) => {
     router.get("/oer_materials", [
         query("text").trim(),
         query("types").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase() : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase() : null)),
         query("licenses").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",") : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",") : null)),
         query("languages").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",") : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",") : null)),
         query("content_languages").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",") : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",") : null)),
         query("provider_ids").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",").map((id) => parseInt(id, 10)) : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",").map(id => parseInt(id, 10)) : null)),
         query("wikipedia").optional().toBoolean(),
         query("wikipedia_limit").optional().toInt(),
         query("limit").optional().toInt(),
-        query("page").optional().toInt(),
-    ], async (req, res, next) => {
+        query("page").optional().toInt()
+    ], async (req: Request, res: Response, next: NextFunction) => {
         // extract the appropriate query parameters
-        let {
-            query: {
-                text,
-                types,
-                languages,
-                content_languages,
-                provider_ids,
-                licenses,
-                wikipedia,
-                wikipedia_limit,
-                limit,
-                page,
-            }
-        } = req;
+        const requestQuery: ISearch = req.query;
+        const {
+            text,
+            types,
+            languages,
+            content_languages,
+            provider_ids,
+            licenses,
+            wikipedia,
+            wikipedia_limit,
+            limit: queryLimit,
+            page: queryPage
+        } = requestQuery;
 
         if (!text) {
             return res.status(400).json({
                 message: "query parameter 'text' not available",
-                query: req.query
+                query: requestQuery
             });
         }
 
@@ -127,27 +124,34 @@ module.exports = (config) => {
         // ------------------------------------
 
         // set default pagination values
-        if (!limit) {
-            limit = DEFAULT_LIMIT;
-        } else if (limit <= 0) {
-            limit = DEFAULT_LIMIT;
-        } else if (limit >= MAX_LIMIT) {
-            limit = MAX_LIMIT;
-        }
+        // which part of the materials do we want to query
+        const limit: number = !queryLimit
+            ? DEFAULT_LIMIT
+            : queryLimit <= 0
+                ? DEFAULT_LIMIT
+                : queryLimit >= MAX_LIMIT
+                    ? DEFAULT_LIMIT
+                    : queryLimit;
+
+        const page: number = !queryPage
+            ? DEFAULT_PAGE
+            : queryPage;
+
+        const size = limit;
+        const from = (page - 1) * size;
+
         req.query.limit = limit;
-        if (!page) {
-            page = DEFAULT_PAGE;
-            req.query.page = page;
-        }
+        req.query.page = page;
 
         // ------------------------------------
         // Set query parameters
         // ------------------------------------
 
         // set the nested must conditions for the "contents" attribute
-        const nestedContentsMust = [{
+        const nestedContentsMust: IQueryElement[] = [{
             term: { "contents.extension": "plain" }
         }];
+
         if (content_languages) {
             nestedContentsMust.push({
                 terms: { "contents.language": content_languages }
@@ -159,16 +163,16 @@ module.exports = (config) => {
         // ------------------------------------
 
         // get the filter parameters (type and language)
-        let typegroup;
-        let filetypes;
+        let typegroup: string;
+        let filetypes: string;
         if (types && ["all", "text", "video", "audio"].includes(types)) {
             typegroup = types === "all" ? null : types;
         } else if (types && types.split(",").length > 0) {
-            filetypes = types.split(",").map((t) => `.*\.${t.trim()}`).join("|");
+            filetypes = types.split(",").map((t:string) => `.*\.${t.trim()}`).join("|");
         }
 
         // add the filter conditions for the regex
-        const filters = [];
+        const filters: IQueryElement[] = [];
         if (filetypes) {
             filters.push({
                 regexp: { material_url: filetypes }
@@ -205,17 +209,13 @@ module.exports = (config) => {
         }
 
         // check if we need to filter the documents
-        const filterFlag = filters.length;
-
-        // which part of the materials do we want to query
-        const size = limit;
-        const from = (page - 1) * size;
+        const filterFlag = filters.length > 0;
 
         // ------------------------------------
         // Translate the user input
         // ------------------------------------
 
-        let translation = text;
+        const translation = text;
 
         // ------------------------------------
         // Set the elasticsearch query body
@@ -253,7 +253,7 @@ module.exports = (config) => {
                             query: {
                                 bool: {
                                     must: [
-                                        { match: { "wikipedia.sec_name": translation } },
+                                        { match: { "wikipedia.sec_name": translation } }
                                     ]
                                 }
                             }
@@ -286,18 +286,20 @@ module.exports = (config) => {
             // get the search results from elasticsearch
             const results = await es.search("oer_materials", esQuery);
             // format the output before sending
-            const output = results.hits.hits.map((hit) => materialFormat(hit, { wikipedia, wikipedia_limit }));
+            const output = results.hits.hits.map((hit: IElasticsearchHit) =>
+                materialFormat(hit, wikipedia, wikipedia_limit)
+            );
 
             // prepare the parameters for the previous query
             const prevQuery = {
                 ...req.query,
-                ...page && { page: page - 1 },
+                ...page && { page: page - 1 }
             };
 
             // prepare the parameters for the next query
             const nextQuery = {
                 ...req.query,
-                ...page && { page: page + 1 },
+                ...page && { page: page + 1 }
             };
 
             const BASE_URL = "https://platform.x5gon.org/api/v1/search";
@@ -306,7 +308,7 @@ module.exports = (config) => {
             const totalPages = Math.ceil(results.hits.total.value / size);
             const prevPage = page - 1 > 0 ? `${BASE_URL}?${querystring.stringify(prevQuery)}` : null;
             const nextPage = totalPages >= page + 1 ? `${BASE_URL}?${querystring.stringify(nextQuery)}` : null;
-            results.aggregations.providers.buckets.forEach((provider) => {
+            results.aggregations.providers.buckets.forEach((provider: { key: string }) => {
                 provider.key = provider.key.toLowerCase();
             });
 
@@ -321,9 +323,9 @@ module.exports = (config) => {
                     next_page: nextPage,
                     aggregations: {
                         licenses: results.aggregations.licenses.buckets,
-                        types: results.aggregations.types.buckets,
                         languages: results.aggregations.languages.buckets,
-                        providers: results.aggregations.providers.buckets
+                        providers: results.aggregations.providers.buckets,
+                        types: results.aggregations.types.buckets
                     }
                 }
             });
@@ -338,7 +340,7 @@ module.exports = (config) => {
      * @apiName esSearchAPI
      * @apiGroup search
      */
-    router.post("/oer_materials", async (req, res, next) => {
+    router.post("/oer_materials", async (req: Request, res: Response, next: NextFunction) => {
         const {
             body: { record }
         } = req;
@@ -353,9 +355,9 @@ module.exports = (config) => {
 
             // modify the license attribute when sending to elasticsearch
             const url = record.license;
-            let shortName;
-            let typedName;
-            let disclaimer = DEFAULT_DISCLAIMER;
+            let shortName: string;
+            let typedName: string[];
+            const disclaimer = DEFAULT_DISCLAIMER;
 
             if (url) {
                 const regex = /\/licen[sc]es\/([\w\-]+)\//;
@@ -372,7 +374,7 @@ module.exports = (config) => {
             };
 
             // modify the wikipedia array
-            for (let value of record.wikipedia) {
+            for (const value of record.wikipedia) {
                 // rename the wikipedia concepts
                 value.sec_uri = value.secUri;
                 value.sec_name = value.secName;
@@ -394,20 +396,24 @@ module.exports = (config) => {
             // refresh the index after pushing the new record
             await es.refreshIndex("oer_materials");
             // return the material id of the added record
-            return res.status(200).json({ message: "record pushed to the index" });
+            return res.status(200).json({
+                message: "record pushed to the index",
+                material_id: record.material_id
+            });
         } catch (error) {
             return next(new ErrorHandler(500, "Internal server error"));
         }
     });
 
+    // get particular material
     router.get("/oer_materials/:material_id", [
         param("material_id").toInt(),
         query("wikipedia").optional().toBoolean(),
-        query("wikipedia_limit").optional().toInt(),
-    ], async (req, res, next) => {
+        query("wikipedia_limit").optional().toInt()
+    ], async (req: Request, res: Response, next: NextFunction) => {
         const {
             params: {
-                material_id
+                material_id: materialId
             },
             query: {
                 wikipedia,
@@ -415,19 +421,22 @@ module.exports = (config) => {
             }
         } = req;
 
-        if (!material_id) {
+        if (!materialId) {
             return res.status(400).json({
                 message: "body parameter material_id not an integer",
-                query: { material_id }
+                params: req.params,
+                query: req.query
             });
         }
 
         try {
             const results = await es.search("oer_materials", {
-                query: { terms: { _id: [material_id] } }
+                query: { terms: { _id: [materialId] } }
             });
             // format the output before sending
-            const output = results.hits.hits.map((hit) => materialFormat(hit, { wikipedia, wikipedia_limit }))[0];
+            const output = results.hits.hits.map((hit: IElasticsearchHit) =>
+                materialFormat(hit, wikipedia, wikipedia_limit)
+            )[0];
 
             // return the status as the response
             return res.status(200).json({
@@ -445,8 +454,8 @@ module.exports = (config) => {
      * @apiGroup search
      */
     router.patch("/oer_materials/:material_id", [
-        param("material_id").toInt(),
-    ], async (req, res, next) => {
+        param("material_id").toInt()
+    ], async (req: Request, res: Response, next: NextFunction) => {
         const {
             params: { material_id },
             body: { record }
@@ -461,7 +470,7 @@ module.exports = (config) => {
 
         try {
             // modify the wikipedia array
-            for (let value of record.wikipedia) {
+            for (const value of record.wikipedia) {
                 // rename the wikipedia concepts
                 value.sec_uri = value.secUri;
                 value.sec_name = value.secName;
@@ -497,7 +506,7 @@ module.exports = (config) => {
      */
     router.delete("/oer_materials/:material_id", [
         param("material_id").toInt()
-    ], async (req, res, next) => {
+    ], async (req: Request, res: Response, next: NextFunction) => {
         const {
             params: { material_id }
         } = req;
diff --git a/src/routes/v1/recommend.js b/src/routes/v1/recommend.ts
similarity index 63%
rename from src/routes/v1/recommend.js
rename to src/routes/v1/recommend.ts
index 6601d48..16a3032 100644
--- a/src/routes/v1/recommend.js
+++ b/src/routes/v1/recommend.ts
@@ -4,59 +4,64 @@
  * manipuating data from Elastic Search.
  */
 
-const router = require("express").Router();
-const { default: Elasticsearch } = require("../../library/elasticsearch");
-const { ErrorHandler } = require("../../library/error");
-
-// internal modules
-const mimetypes = require("../../config/mimetypes");
-
+import {
+    IConfiguration,
+    IElasticsearchHit,
+    ISearch,
+    IQueryElement
+} from "../../Interfaces";
+
+import { Router, Request, Response, NextFunction } from "express";
 // validating the query parameters
-const { query, body, param } = require("express-validator");
-
+import { query } from "express-validator";
 // creation of the query string to help the user navigate through
-const querystring = require("querystring");
-
-/**
- * Returns the general material type.
- * @param {String} mimetype - The document mimetype.
- * @returns {String|Null} The material type.
- */
-function materialType(mimetype) {
-    for (let type in mimetypes) {
-        if (mimetypes[type].includes(mimetype)) {
-            return type;
-        }
-    }
-    return null;
-}
-
-function materialFormat(hit, { wikipedia, wikipedia_limit }) {
+import * as querystring from "querystring";
+// add error handling functionality
+import { ErrorHandler } from "../../library/error";
+// import elasticsearch module
+import Elasticsearch from "../../library/elasticsearch";
+
+// initialize the express router
+const router = Router();
+
+// format the material
+function materialFormat(
+    hit: IElasticsearchHit,
+    wikipedia?: boolean,
+    wikipedia_limit?: number
+) {
     return {
         weight: hit._score,
+        material_id: hit._source.material_id,
         title: hit._source.title,
         description: hit._source.description,
         creation_date: hit._source.creation_date,
         retrieved_date: hit._source.retrieved_date,
         type: hit._source.type,
         mimetype: hit._source.mimetype,
+        url: hit._source.material_url,
         website: hit._source.website_url,
         language: hit._source.language,
         license: hit._source.license,
         provider: {
             id: hit._source.provider_id,
             name: hit._source.provider_name.toLowerCase(),
-            domain: hit._source.provider_url,
-        }
+            domain: hit._source.provider_url
+        },
+        content_ids: hit._source.contents
+            ? hit._source.contents.map(content => content.content_id)
+            : [],
+        ...(wikipedia && {
+            wikipedia:
+                wikipedia_limit && wikipedia_limit > 0
+                    ? hit._source.wikipedia.slice(0, wikipedia_limit)
+                    : hit._source.wikipedia
+        })
     };
 }
 
-/**
- * @description Assign the elasticsearch API routes.
- * @param {Object} config - The configuration object.
- * @returns {Object} The search router.
- */
-module.exports = (config) => {
+// assign the recommendation API routes
+export default (config: IConfiguration) => {
     // set the default parameters
     const DEFAULT_LIMIT = 20;
     const MAX_LIMIT = 100;
@@ -65,60 +70,47 @@ module.exports = (config) => {
     // esablish connection with elasticsearch
     const es = new Elasticsearch(config.elasticsearch);
 
-    let setLanguages = [];
-    es.search("oer_materials", {
-        size: 0,
-        aggregations: {
-            languages: {
-                terms: { field: "language" }
-            },
-        }
-    }).then(({ aggregations }) => {
-        setLanguages = aggregations.languages.buckets
-            .map((obj) => obj.key);
-    });
-
     /**
      * @api {GET} /api/v1/oer_materials Search through the OER materials
      * @apiVersion 1.0.0
      * @apiName searchAPI
      * @apiGroup search
      */
+    // TODO: must specify the correct material type
     router.get("/recommend/bundles", [
         query("text").trim(),
         query("url").trim(),
         query("types").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase() : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase() : null)),
         query("licenses").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",") : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",") : null)),
         query("languages").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",") : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",") : null)),
         query("content_languages").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",") : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",") : null)),
         query("provider_ids").optional().trim()
-            .customSanitizer((value) => (value && value.length ? value.toLowerCase().split(",").map((id) => parseInt(id, 10)) : null)),
+            .customSanitizer((value: string) => (value && value.length ? value.toLowerCase().split(",").map(id => parseInt(id, 10)) : null)),
         query("wikipedia").optional().toBoolean(),
         query("wikipedia_limit").optional().toInt(),
         query("limit").optional().toInt(),
-        query("page").optional().toInt(),
-    ], async (req, res, next) => {
-
+        query("page").optional().toInt()
+    ], async (req: Request, res: Response, next: NextFunction) => {
         // extract the appropriate query parameters
-        let {
-            query: {
-                text,
-                url,
-                types,
-                languages,
-                content_languages,
-                provider_ids,
-                licenses,
-                wikipedia,
-                wikipedia_limit,
-                limit,
-                page,
-            }
-        } = req;
+        const requestQuery: ISearch = req.query;
+        // extract the appropriate query parameters
+        const {
+            text,
+            url,
+            types,
+            languages,
+            content_languages,
+            provider_ids,
+            licenses,
+            wikipedia,
+            wikipedia_limit,
+            limit: queryLimit,
+            page: queryPage
+        } = requestQuery;
 
         if (!text && !url) {
             return res.status(400).json({
@@ -138,9 +130,8 @@ module.exports = (config) => {
             }
         };
 
-        let wikiConcepts;
-        let materialURLs;
-        let preferedLangs;
+        let wikiConcepts: [string, number][];
+        let materialURLs: string[];
         try {
             // get the search results from elasticsearch
             const results = await es.search("oer_materials", materialQuery);
@@ -149,24 +140,23 @@ module.exports = (config) => {
                 return res.redirect(`/api/v1/oer_materials?${queryParams}`);
             }
 
-            const viewedMaterials = results.hits.hits;
-            const viewedLangauges = viewedMaterials.map((hit) => hit._source.language);
-            materialURLs = viewedMaterials.map((hit) => hit._source.material_url);
-            preferedLangs = setLanguages.filter((lang) => !viewedLangauges.includes(lang));
+            const viewedMaterials: IElasticsearchHit[] = results.hits.hits;
+            materialURLs = viewedMaterials.map(hit => hit._source.material_url);
             // return res.json(materialURLs);
-            wikiConcepts = viewedMaterials
-                .map((hit) => hit._source.wikipedia.slice(0, 30).map((wiki) => wiki.sec_name))
+            wikiConcepts = Object.entries(viewedMaterials
+                .map(hit => hit._source.wikipedia.slice(0, 30).map(wiki => wiki.sec_name))
                 .reduce((prev, curr) => prev.concat(curr), [])
                 .reduce((prev, curr) => {
                     if (!prev[curr]) {
-                        prev[curr] = 1;
+                        prev[curr] = 0;
                     }
                     prev[curr] += 1;
                     return prev;
-                }, {});
+                }, {}));
 
             const startSlice = wikiConcepts.length > 2 ? 2 : 0;
-            wikiConcepts = Object.entries(wikiConcepts).sort((a, b) => b[1] - a[1])
+            wikiConcepts = wikiConcepts
+                .sort((a, b) => b[1] - a[1])
                 .slice(startSlice, 20);
         } catch (error) {
             return next(new ErrorHandler(500, "Internal server error"));
@@ -177,27 +167,34 @@ module.exports = (config) => {
         // ------------------------------------
 
         // set default pagination values
-        if (!limit) {
-            limit = DEFAULT_LIMIT;
-        } else if (limit <= 0) {
-            limit = DEFAULT_LIMIT;
-        } else if (limit >= MAX_LIMIT) {
-            limit = MAX_LIMIT;
-        }
+        // which part of the materials do we want to query
+        const limit: number = !queryLimit
+            ? DEFAULT_LIMIT
+            : queryLimit <= 0
+                ? DEFAULT_LIMIT
+                : queryLimit >= MAX_LIMIT
+                    ? DEFAULT_LIMIT
+                    : queryLimit;
+
+        const page: number = !queryPage
+            ? DEFAULT_PAGE
+            : queryPage;
+
+        const size = limit;
+        const from = (page - 1) * size;
+
         req.query.limit = limit;
-        if (!page) {
-            page = DEFAULT_PAGE;
-            req.query.page = page;
-        }
+        req.query.page = page;
 
         // ------------------------------------
         // Set query parameters
         // ------------------------------------
 
         // set the nested must conditions for the "contents" attribute
-        const nestedContentsMust = [{
+        const nestedContentsMust: IQueryElement[] = [{
             term: { "contents.extension": "plain" }
         }];
+
         if (content_languages) {
             nestedContentsMust.push({
                 terms: { "contents.language": content_languages }
@@ -209,24 +206,27 @@ module.exports = (config) => {
         // ------------------------------------
 
         // get the filter parameters (type and language)
-        let typegroup;
-        let filetypes;
+        let typegroup: string;
+        let filetypes: string;
         if (types && ["all", "text", "video", "audio"].includes(types)) {
             typegroup = types === "all" ? null : types;
         } else if (types && types.split(",").length > 0) {
-            filetypes = types.split(",").map((t) => `.*\.${t.trim()}`).join("|");
+            filetypes = types
+                .split(",")
+                .map(t => `.*\.${t.trim()}`)
+                .join("|");
         }
 
         //  add the must not filter conditions
-        const filtersMustNot = [];
+        const filtersMustNot: IQueryElement[] = [];
         if (materialURLs) {
             filtersMustNot.push({
                 terms: { material_url: materialURLs }
-            })
+            });
         }
 
         // add the filter conditions for the regex
-        const filtersMust = [];
+        const filtersMust: IQueryElement[] = [];
         if (filetypes) {
             filtersMust.push({
                 regexp: { material_url: filetypes }
@@ -263,11 +263,7 @@ module.exports = (config) => {
         }
 
         // check if we need to filter the documents
-        const filterFlag = filtersMust.length || filtersMustNot.length;
-
-        // which part of the materials do we want to query
-        const size = limit;
-        const from = (page - 1) * size;
+        const filterFlag = filtersMust.length > 0 || filtersMustNot.length > 0;
 
         // ------------------------------------
         // Set the elasticsearch query body
@@ -287,7 +283,7 @@ module.exports = (config) => {
             },
             query: {
                 bool: {
-                    should: wikiConcepts.map((wiki) => ({
+                    should: wikiConcepts.map(wiki => ({
                         nested: {
                             path: "wikipedia",
                             query: {
@@ -296,18 +292,18 @@ module.exports = (config) => {
                                         query: wiki[0],
                                         boost: wiki[1] / materialURLs.length
                                     }
-                                },
+                                }
                             }
                         }
                     })),
-                    ...filterFlag && {
+                    ...(filterFlag && {
                         filter: {
                             bool: {
-                                ...filtersMust && { must: filtersMust },
-                                ...filtersMustNot && { must_not: filtersMustNot }
+                                ...(filtersMust && { must: filtersMust }),
+                                ...(filtersMustNot && { must_not: filtersMustNot })
                             }
                         }
-                    }
+                    })
                 }
             },
             collapse: {
@@ -336,27 +332,36 @@ module.exports = (config) => {
             const results = await es.search("oer_materials", esQuery);
             // return res.json(results);
             // format the output before sending
-            const output = results.hits.hits.map((hit) => materialFormat(hit, { wikipedia, wikipedia_limit }));
+            const output = results.hits.hits.map((hit: IElasticsearchHit) =>
+                materialFormat(hit, wikipedia, wikipedia_limit)
+            );
 
             // prepare the parameters for the previous query
             const prevQuery = {
                 ...req.query,
-                ...page && { page: page - 1 },
+                ...(page && { page: page - 1 })
             };
 
             // prepare the parameters for the next query
             const nextQuery = {
                 ...req.query,
-                ...page && { page: page + 1 },
+                ...(page && { page: page + 1 })
             };
 
-            const BASE_URL = "https://platform.x5gon.org/api/v1/recommend/materials";
+            const BASE_URL =
+                "https://platform.x5gon.org/api/v1/recommend/materials";
             // prepare the metadata used to navigate through the search
             const totalHits = results.hits.total.value;
             const totalPages = Math.ceil(results.hits.total.value / size);
-            const prevPage = page - 1 > 0 ? `${BASE_URL}?${querystring.stringify(prevQuery)}` : null;
-            const nextPage = totalPages >= page + 1 ? `${BASE_URL}?${querystring.stringify(nextQuery)}` : null;
-            results.aggregations.providers.buckets.forEach((provider) => {
+            const prevPage =
+                page - 1 > 0
+                    ? `${BASE_URL}?${querystring.stringify(prevQuery)}`
+                    : null;
+            const nextPage =
+                totalPages >= page + 1
+                    ? `${BASE_URL}?${querystring.stringify(nextQuery)}`
+                    : null;
+            results.aggregations.providers.buckets.forEach(provider => {
                 provider.key = provider.key.toLowerCase();
             });
 
@@ -380,7 +385,8 @@ module.exports = (config) => {
         } catch (error) {
             return next(new ErrorHandler(500, "Internal server error"));
         }
-    });
+    }
+    );
 
     // return the router
     return router;
diff --git a/tsconfig.json b/tsconfig.json
index 21e0e38..7d440e1 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -7,6 +7,7 @@
         "lib": ["es2017"],
         "noImplicitReturns": true,
         "noFallthroughCasesInSwitch": true,
+        "resolveJsonModule": true,
         "alwaysStrict": true,
         "noUnusedLocals": true,
         "pretty": false,
diff --git a/tslint.json b/tslint.json
index ac2c48d..39a8943 100644
--- a/tslint.json
+++ b/tslint.json
@@ -19,9 +19,8 @@
     },
     "linterOptions": {
       "exclude": [
-        "public/**/*.js",
-        "config/**/*.js",
-        "node_modules/**/*.ts"
+        "node_modules/**/*.ts",
+        "src/load/*.js"
       ]
     }
   }