feat(client): ts-migrate client/src/utils (#42666)

* rename js files to ts

* start migrating ajax

* finish migrating ajax

* migrate algolia-locale-setup

* migrate format

* migrate format.test

* migrate get-words

* install axios for types in handled-error

* migrate handled-error

* migrate handled-error.test

* migrate report-error

* migrate script-loaders

* migrate to-learn-path

* correct renamed imports

* remove unnecessary type assertions in searchBar

* remove unnecessary global comment

* remove unnecessary max-len enable/disable

* change axios imports to type imports

* revert to .then() from await

* use UserType from redux/prop-types

* replace assertion with generic type

* revert format to JS

* remove unused getArticleById()

* update putUpdateUserFlag() to use Record

* remove unnecessary envData cast

* update algolia-locale-setup types

* remove invalid key property

client/package.json

@@ -150,6 +150,7 @@
     "@types/store": "2.0.2",
     "@types/validator": "13.6.3",
     "autoprefixer": "10.3.0",
+    "axios": "^0.21.1",
     "babel-plugin-transform-imports": "2.0.0",
     "chokidar": "3.5.2",
     "copy-webpack-plugin": "9.0.1",

client/src/client-only-routes/show-certification.tsx

@@ -22,8 +22,8 @@ import {
 } from '../redux';
 import { certMap } from '../resources/cert-and-project-map';
 import { createFlashMessage } from '../components/Flash/redux';
-import standardErrorMessage from '../utils/standardErrorMessage';
+import standardErrorMessage from '../utils/standard-error-message';
-import reallyWeirdErrorMessage from '../utils/reallyWeirdErrorMessage';
+import reallyWeirdErrorMessage from '../utils/really-weird-error-message';
 import { langCodes } from '../../../config/i18n/all-langs';
 import envData from '../../../config/env.json';
 

client/src/components/Donation/PayPalButtonScriptLoader.js

@@ -4,7 +4,7 @@ import React, { Component } from 'react';
 import ReactDOM from 'react-dom';
 import PropTypes from 'prop-types';
 
-import { scriptLoader, scriptRemover } from '../../utils/scriptLoaders';
+import { scriptLoader, scriptRemover } from '../../utils/script-loaders';
 import { Loader } from '../../components/helpers';
 
 export class PayPalButtonScriptLoader extends Component {

client/src/components/search/searchBar/search-bar-optimized.tsx

@@ -6,7 +6,7 @@ import { searchPageUrl } from '../../../utils/algolia-locale-setup';
 const SearchBarOptimized = (): JSX.Element => {
   const { t } = useTranslation();
   const placeholder = t('search.placeholder');
-  const searchUrl: string = searchPageUrl as string;
+  const searchUrl = searchPageUrl;
   const [value, setValue] = useState('');
   const onChange = (event: React.ChangeEvent<HTMLInputElement>) =>
     setValue(event.target.value);

client/src/components/search/searchBar/search-bar.tsx

@@ -23,7 +23,7 @@ import SearchHits from './search-hits';
 import './searchbar-base.css';
 import './searchbar.css';
 
-const searchUrl: string = searchPageUrl as string;
+const searchUrl = searchPageUrl;
 const mapStateToProps = createSelector(
   isSearchDropdownEnabledSelector,
   isSearchBarFocusedSelector,

client/src/components/search/searchBar/search-hits.tsx

@@ -7,7 +7,7 @@ import { searchPageUrl } from '../../../utils/algolia-locale-setup';
 import Suggestion from './search-suggestion';
 import NoHitsSuggestion from './no-hits-suggestion';
 
-const searchUrl = searchPageUrl as string;
+const searchUrl = searchPageUrl;
 interface customHitsPropTypes {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   hits: Array<any>;

client/src/redux/error-saga.js

@@ -5,7 +5,7 @@ import { isError } from 'lodash-es';
 import { isHandledError, unwrapHandledError } from '../utils/handled-error';
 import { reportClientSideError } from '../utils/report-error';
 import { createFlashMessage } from '../components/Flash/redux';
-import reportedErrorMessage from '../utils/reportedErrorMessage';
+import reportedErrorMessage from '../utils/reported-error-message';
 
 const errorActionSelector = action => isError(action.payload);
 

client/src/redux/settings/update-email-saga.js

@@ -5,7 +5,7 @@ import { updateMyEmailComplete, updateMyEmailError } from './';
 import { createFlashMessage } from '../../components/Flash/redux';
 
 import { putUserUpdateEmail } from '../../utils/ajax';
-import reallyWeirdErrorMessage from '../../utils/reallyWeirdErrorMessage';
+import reallyWeirdErrorMessage from '../../utils/really-weird-error-message';
 
 function* updateMyEmailSaga({ payload: email = '' }) {
   if (!email || !isEmail(email)) {

client/src/templates/Challenges/components/Side-Panel.js

@@ -10,7 +10,7 @@ import TestSuite from './Test-Suite';
 import { challengeTestsSelector, isChallengeCompletedSelector } from '../redux';
 import { createSelector } from 'reselect';
 import './side-panel.css';
-import { mathJaxScriptLoader } from '../../../utils/scriptLoaders';
+import { mathJaxScriptLoader } from '../../../utils/script-loaders';
 
 const mapStateToProps = createSelector(
   isChallengeCompletedSelector,

client/src/utils/ajax.js

@@ -1,118 +0,0 @@
-import envData from '../../../config/env.json';
-import Tokens from 'csrf';
-import cookies from 'browser-cookies';
-
-const { apiLocation } = envData;
-
-const base = apiLocation;
-const tokens = new Tokens();
-
-const defaultOptions = {
-  credentials: 'include'
-};
-
-// _csrf is passed to the client as a cookie. Tokens are sent back to the server
-// via headers:
-function getCSRFToken() {
-  const _csrf = typeof window !== 'undefined' && cookies.get('_csrf');
-  if (!_csrf) {
-    return '';
-  } else {
-    return tokens.create(_csrf);
-  }
-}
-
-function get(path) {
-  return fetch(`${base}${path}`, defaultOptions).then(res => res.json());
-}
-
-export function post(path, body) {
-  return request('POST', path, body);
-}
-
-function put(path, body) {
-  return request('PUT', path, body);
-}
-
-function request(method, path, body) {
-  const options = {
-    ...defaultOptions,
-    method,
-    headers: {
-      'CSRF-Token': getCSRFToken(),
-      'Content-Type': 'application/json'
-    },
-    body: JSON.stringify(body)
-  };
-  return fetch(`${base}${path}`, options).then(res => res.json());
-}
-
-/** GET **/
-
-export function getSessionUser() {
-  return get('/user/get-session-user');
-}
-
-export function getUserProfile(username) {
-  return get(`/api/users/get-public-profile?username=${username}`);
-}
-
-export function getShowCert(username, certSlug) {
-  return get(`/certificate/showCert/${username}/${certSlug}`);
-}
-
-export function getUsernameExists(username) {
-  return get(`/api/users/exists?username=${username}`);
-}
-
-export function getArticleById(shortId) {
-  return get(`/n/${shortId}`);
-}
-
-/** POST **/
-
-export function addDonation(body) {
-  return post('/donate/add-donation', body);
-}
-
-export function postReportUser(body) {
-  return post('/user/report-user', body);
-}
-
-export function postDeleteAccount(body) {
-  return post('/account/delete', body);
-}
-
-export function postResetProgress(body) {
-  return post('/account/reset-progress', body);
-}
-
-/** PUT **/
-
-export function putUpdateMyAbout(values) {
-  return put('/update-my-about', { ...values });
-}
-
-export function putUpdateMyUsername(username) {
-  return put('/update-my-username', { username });
-}
-
-export function putUpdateMyProfileUI(profileUI) {
-  return put('/update-my-profileui', { profileUI });
-}
-
-export function putUpdateUserFlag(update) {
-  return put('/update-user-flag', update);
-}
-
-export function putUserAcceptsTerms(quincyEmails) {
-  return put('/update-privacy-terms', { quincyEmails });
-}
-
-export function putUserUpdateEmail(email) {
-  return put('/update-my-email', { email });
-}
-
-export function putVerifyCert(certSlug) {
-  return put('/certificate/verify', { certSlug });
-}

client/src/utils/ajax.ts

@@ -0,0 +1,160 @@
+import envData from '../../../config/env.json';
+import Tokens from 'csrf';
+import cookies from 'browser-cookies';
+
+import type { UserType } from '../redux/prop-types';
+
+const { apiLocation } = envData;
+
+const base = apiLocation;
+const tokens = new Tokens();
+
+const defaultOptions: RequestInit = {
+  credentials: 'include'
+};
+
+// _csrf is passed to the client as a cookie. Tokens are sent back to the server
+// via headers:
+function getCSRFToken() {
+  const _csrf = typeof window !== 'undefined' && cookies.get('_csrf');
+  if (!_csrf) {
+    return '';
+  } else {
+    return tokens.create(_csrf);
+  }
+}
+
+async function get<T>(path: string): Promise<T> {
+  return fetch(`${base}${path}`, defaultOptions).then<T>(res => res.json());
+}
+
+export function post<T = void>(path: string, body: unknown): Promise<T> {
+  return request('POST', path, body);
+}
+
+function put<T = void>(path: string, body: unknown): Promise<T> {
+  return request('PUT', path, body);
+}
+
+async function request<T>(
+  method: 'POST' | 'PUT',
+  path: string,
+  body: unknown
+): Promise<T> {
+  const options: RequestInit = {
+    ...defaultOptions,
+    method,
+    headers: {
+      'CSRF-Token': getCSRFToken(),
+      'Content-Type': 'application/json'
+    },
+    body: JSON.stringify(body)
+  };
+  return fetch(`${base}${path}`, options).then<T>(res => res.json());
+}
+
+/** GET **/
+
+interface SessionUser {
+  user: UserType;
+  sessionMeta: { activeDonations: number };
+  result: string;
+}
+export function getSessionUser(): Promise<SessionUser> {
+  return get('/user/get-session-user');
+}
+
+export function getUserProfile(username: string): Promise<UserType> {
+  return get(`/api/users/get-public-profile?username=${username}`);
+}
+
+interface Cert {
+  certTitle: string;
+  username: string;
+  date: Date;
+  completionTime: string;
+}
+export function getShowCert(username: string, certSlug: string): Promise<Cert> {
+  return get(`/certificate/showCert/${username}/${certSlug}`);
+}
+
+export function getUsernameExists(username: string): Promise<boolean> {
+  return get(`/api/users/exists?username=${username}`);
+}
+
+/** POST **/
+
+interface Donation {
+  email: string;
+  amount: number;
+  duration: string;
+  provider: string;
+  subscriptionId: string;
+  customerId: string;
+  startDate: Date;
+}
+export function addDonation(body: Donation): Promise<void> {
+  return post('/donate/add-donation', body);
+}
+
+interface Report {
+  username: string;
+  reportDescription: string;
+}
+export function postReportUser(body: Report): Promise<void> {
+  return post('/user/report-user', body);
+}
+
+// Both are called without a payload in danger-zone-saga,
+// which suggests both are sent without any body
+// TODO: Convert to DELETE
+export function postDeleteAccount(): Promise<void> {
+  return post('/account/delete', {});
+}
+
+export function postResetProgress(): Promise<void> {
+  return post('/account/reset-progress', {});
+}
+
+/** PUT **/
+
+interface MyAbout {
+  name: string;
+  location: string;
+  about: string;
+  picture: string;
+}
+export function putUpdateMyAbout(values: MyAbout): Promise<void> {
+  return put('/update-my-about', { ...values });
+}
+
+export function putUpdateMyUsername(username: string): Promise<void> {
+  return put('/update-my-username', { username });
+}
+
+export function putUpdateMyProfileUI(
+  profileUI: UserType['profileUI']
+): Promise<void> {
+  return put('/update-my-profileui', { profileUI });
+}
+
+// Update should contain only one flag and one new value
+// It's possible to constrain to only one key with TS, but is overkill for this
+// https://stackoverflow.com/a/60807986
+export function putUpdateUserFlag(
+  update: Record<string, string>
+): Promise<void> {
+  return put('/update-user-flag', update);
+}
+
+export function putUserAcceptsTerms(quincyEmails: boolean): Promise<void> {
+  return put('/update-privacy-terms', { quincyEmails });
+}
+
+export function putUserUpdateEmail(email: string): Promise<void> {
+  return put('/update-my-email', { email });
+}
+
+export function putVerifyCert(certSlug: string): Promise<void> {
+  return put('/certificate/verify', { certSlug });
+}

client/src/utils/algolia-locale-setup.ts

@@ -1,6 +1,8 @@
 import envData from '../../../config/env.json';
 
-const { clientLocale } = envData;
+const { clientLocale } = envData as {
+  clientLocale: keyof typeof algoliaIndices;
+};
 
 const algoliaIndices = {
   english: {

client/src/utils/curriculum-helpers.test.ts

@@ -2,9 +2,7 @@ import __testHelpers, { removeJSComments } from './curriculum-helpers';
 import jsTestValues from './__fixtures/curriculum-helpers-javascript';
 import cssTestValues from './__fixtures/curriculum-helpers-css';
 import htmlTestValues from './__fixtures/curriculum-helpers-html';
-/* eslint-disable max-len */
 import whiteSpaceTestValues from './__fixtures/curriculum-helpers-remove-white-space';
-/* eslint-enable max-len */
 
 const { stringWithWhiteSpaceChars, stringWithWhiteSpaceCharsRemoved } =
   whiteSpaceTestValues;

client/src/utils/format.test.ts

@@ -1,12 +1,9 @@
-/* global BigInt */
+import { format } from './format';
 
-const { format } = require('./format');
-
-/* eslint-disable no-unused-vars */
 function simpleFun() {
+  // eslint-disable-next-line no-var, @typescript-eslint/no-unused-vars
   var x = 'y';
 }
-/* eslint-enable no-unused-vars */
 
 /* format uses util.inspect to do almost everything, the tests are just there
 to warn us if util.inspect ever changes */

client/src/utils/get-words.ts

@@ -1,8 +1,18 @@
-/* global preval */
-
 // this lets us do dynamic work ahead of time, inlining motivation.json, so
 // that Webpack will never try to include locales that we know are not used.
 
+interface Quote {
+  quote: string;
+  author: string;
+}
+
+interface Motivation {
+  compliments: string[];
+  motivationalQuotes: Quote[];
+}
+
+declare const preval: (s: TemplateStringsArray) => Motivation;
+
 const words = preval`
   const config = require('../../../config/env.json');
   const { clientLocale } = config;
@@ -11,14 +21,14 @@ const words = preval`
   module.exports = words;
 `;
 
-function randomItem(arr) {
+function randomItem<T>(arr: T[]): T {
   return arr[Math.floor(Math.random() * arr.length)];
 }
 
-export function randomQuote() {
+export function randomQuote(): Quote {
   return randomItem(words.motivationalQuotes);
 }
 
-export function randomCompliment() {
+export function randomCompliment(): string {
   return randomItem(words.compliments);
 }

client/src/utils/handled-error.js

@@ -1,82 +0,0 @@
-import { has } from 'lodash-es';
-
-import standardErrorMessage from './standardErrorMessage';
-import reportedErrorMessage from './reportedErrorMessage';
-
-import { reportClientSideError } from './report-error';
-
-export const handledErrorSymbol = Symbol('handledError');
-
-export function isHandledError(err) {
-  return has(err, handledErrorSymbol);
-}
-
-export function unwrapHandledError(err) {
-  return handledErrorSymbol in err ? err[handledErrorSymbol] : {};
-}
-
-export function wrapHandledError(err, { type, message, redirectTo }) {
-  err[handledErrorSymbol] = { type, message, redirectTo };
-  return err;
-}
-
-export function handle400Error(e, options = { redirectTo: '/' }) {
-  const {
-    response: { status }
-  } = e;
-  let { redirectTo } = options;
-  let flash = { ...standardErrorMessage, redirectTo };
-
-  switch (status) {
-    case 401:
-    case 403: {
-      return {
-        ...flash,
-        type: 'warn',
-        message: 'flash.not-authorized'
-      };
-    }
-    case 404: {
-      return {
-        ...flash,
-        type: 'info',
-        message: 'flash.could-not-find'
-      };
-    }
-    default: {
-      return flash;
-    }
-  }
-}
-
-export function handle500Error(
-  e,
-  options = {
-    redirectTo: '/'
-  },
-  _reportClientSideError = reportClientSideError
-) {
-  const { redirectTo } = options;
-  _reportClientSideError(e, 'We just handled a 5** error on the client');
-  return { ...reportedErrorMessage, redirectTo };
-}
-
-export function handleAPIError(
-  e,
-  options,
-  _reportClientSideError = reportClientSideError
-) {
-  const { response: { status = 0 } = {} } = e;
-  if (status >= 400 && status < 500) {
-    return handle400Error(e, options);
-  }
-  if (status >= 500) {
-    return handle500Error(e, options, _reportClientSideError);
-  }
-  const { redirectTo } = options;
-  _reportClientSideError(
-    e,
-    'We just handled an api error on the client without an error status code'
-  );
-  return { ...reportedErrorMessage, redirectTo };
-}

client/src/utils/handled-error.test.ts

@@ -1,4 +1,6 @@
 import { isObject } from 'lodash-es';
+import type { AxiosError } from 'axios';
+
 import {
   isHandledError,
   wrapHandledError,
@@ -6,8 +8,9 @@ import {
   handledErrorSymbol,
   handleAPIError
 } from './handled-error';
+import type { HandledError } from './handled-error';
 
-import reportedErrorMessage from './reportedErrorMessage';
+import reportedErrorMessage from './reported-error-message';
 
 describe('client/src utilities', () => {
   describe('handled-error.js', () => {
@@ -19,7 +22,7 @@ describe('client/src utilities', () => {
 
     describe('isHandledError', () => {
       it('returns a boolean', () => {
-        expect(typeof isHandledError({})).toEqual('boolean');
+        expect(typeof isHandledError({} as Error)).toEqual('boolean');
       });
 
       it('returns false for an unhandled error', () => {
@@ -27,7 +30,7 @@ describe('client/src utilities', () => {
       });
 
       it('returns true for a handled error', () => {
-        const handledError = new Error();
+        const handledError = new Error() as HandledError;
         handledError[handledErrorSymbol] = {};
 
         expect(isHandledError(handledError)).toEqual(true);
@@ -39,14 +42,14 @@ describe('client/src utilities', () => {
       // we need to make these tests more robust 💪
       it('returns an error with a handledError property', () => {
         const handledError = wrapHandledError(
-          new Error(),
+          new Error() as HandledError,
           mockHandledErrorData
         );
         expect(handledErrorSymbol in handledError).toEqual(true);
       });
       it('assigns error handling details to the handledError property', () => {
         const handledError = wrapHandledError(
-          new Error(),
+          new Error() as HandledError,
           mockHandledErrorData
         );
         expect(handledError[handledErrorSymbol]).toEqual(mockHandledErrorData);
@@ -57,13 +60,13 @@ describe('client/src utilities', () => {
       // this is testing implementation details 👎
       // we need to make these tests more robust 💪
       it('returns an object by default', () => {
-        const error = new Error();
+        const error = new Error() as HandledError;
         const unwrappedError = unwrapHandledError(error);
         expect(isObject(unwrappedError)).toBe(true);
       });
 
       it('returns the data that was wrapped in the error', () => {
-        const handledError = new Error();
+        const handledError = new Error() as HandledError;
         handledError[handledErrorSymbol] = mockHandledErrorData;
         const unwrapped = unwrapHandledError(handledError);
         expect(unwrapped).toEqual(mockHandledErrorData);
@@ -71,7 +74,7 @@ describe('client/src utilities', () => {
     });
 
     describe('handleAPIError', () => {
-      let reportMock;
+      let reportMock: () => void;
       beforeEach(() => {
         reportMock = jest.fn();
       });
@@ -82,7 +85,7 @@ describe('client/src utilities', () => {
           response: {
             status: 400
           }
-        };
+        } as AxiosError;
         const result = handleAPIError(
           axiosErrorMock,
           { redirectTo: '/' },
@@ -100,7 +103,7 @@ describe('client/src utilities', () => {
             response: {
               status: i
             }
-          };
+          } as AxiosError;
           handleAPIError(axiosErrorMock, { redirectTo: '/' }, reportMock);
         }
         expect(reportMock).not.toHaveBeenCalled();
@@ -111,7 +114,7 @@ describe('client/src utilities', () => {
           response: {
             status: 502
           }
-        };
+        } as AxiosError;
         handleAPIError(axiosErrorMock, { redirectTo: '/' }, reportMock);
         expect(reportMock).toHaveBeenCalledTimes(1);
       });
@@ -121,7 +124,7 @@ describe('client/src utilities', () => {
           response: {
             status: 502
           }
-        };
+        } as AxiosError;
         const result = handleAPIError(
           axiosErrorMock,
           { redirectTo: '/' },
@@ -135,7 +138,7 @@ describe('client/src utilities', () => {
           response: {
             status: 400
           }
-        };
+        } as AxiosError;
         const result = handleAPIError(
           axiosErrorMock,
           { redirectTo: null },

client/src/utils/handled-error.ts

@@ -0,0 +1,109 @@
+import { has } from 'lodash-es';
+import type { AxiosError, AxiosResponse } from 'axios';
+
+import standardErrorMessage from './standard-error-message';
+import reportedErrorMessage from './reported-error-message';
+
+import { reportClientSideError } from './report-error';
+
+interface ErrorData {
+  type?: string;
+  message?: string;
+  redirectTo?: string | null;
+}
+
+export const handledErrorSymbol = Symbol('handledError');
+
+export type HandledError = Error & {
+  [handledErrorSymbol]: ErrorData;
+};
+
+export function isHandledError(err: unknown): err is HandledError {
+  return has(err, handledErrorSymbol);
+}
+
+export function unwrapHandledError(
+  err: HandledError
+): ErrorData | Record<string, never> {
+  return handledErrorSymbol in err ? err[handledErrorSymbol] : {};
+}
+
+export function wrapHandledError(
+  err: Error,
+  { type, message, redirectTo }: ErrorData
+): HandledError {
+  (err as HandledError)[handledErrorSymbol] = {
+    type,
+    message,
+    redirectTo
+  };
+  return err as HandledError;
+}
+
+export function handle400Error(
+  e: AxiosError,
+  options: ErrorData = { redirectTo: '/' }
+): ErrorData {
+  const { status } = e.response as AxiosResponse;
+  const { redirectTo } = options;
+  const flash = { ...standardErrorMessage, redirectTo };
+
+  switch (status) {
+    case 401:
+    case 403: {
+      return {
+        ...flash,
+        type: 'warn',
+        message: 'flash.not-authorized'
+      };
+    }
+    case 404: {
+      return {
+        ...flash,
+        type: 'info',
+        message: 'flash.could-not-find'
+      };
+    }
+    default: {
+      return flash;
+    }
+  }
+}
+
+export function handle500Error(
+  e: AxiosError,
+  options: ErrorData = {
+    redirectTo: '/'
+  },
+  _reportClientSideError: (
+    e: Error,
+    message: string
+  ) => void = reportClientSideError
+): ErrorData {
+  const { redirectTo } = options;
+  _reportClientSideError(e, 'We just handled a 5** error on the client');
+  return { ...reportedErrorMessage, redirectTo };
+}
+
+export function handleAPIError(
+  e: AxiosError,
+  options: ErrorData,
+  _reportClientSideError: (
+    e: Error,
+    message: string
+  ) => void = reportClientSideError
+): ErrorData {
+  const { response: { status = 0 } = {} } = e;
+  if (status >= 400 && status < 500) {
+    return handle400Error(e, options);
+  }
+  if (status >= 500) {
+    return handle500Error(e, options, _reportClientSideError);
+  }
+  const { redirectTo } = options;
+  _reportClientSideError(
+    e,
+    'We just handled an api error on the client without an error status code'
+  );
+  return { ...reportedErrorMessage, redirectTo };
+}

client/src/utils/path-parsers.test.ts

@@ -1,5 +1,3 @@
-/* global describe it expect */
-
 import { isChallenge, isLanding } from './path-parsers';
 
 const pathnames = {

client/src/utils/report-error.js

@@ -1,4 +0,0 @@
-// TODO: integrate with Sentry?
-export function reportClientSideError(e, message = 'Unhandled error') {
-  return console.error(`Client: ${message}`, e);
-}

client/src/utils/report-error.ts

@@ -0,0 +1,7 @@
+// TODO: integrate with Sentry?
+export function reportClientSideError(
+  e: Error,
+  message = 'Unhandled error'
+): void {
+  return console.error(`Client: ${message}`, e);
+}

client/src/utils/script-loaders.ts

@@ -1,25 +1,29 @@
-export const scriptLoader = (id, key, async, src, onload, text) => {
+export function scriptLoader(
-  let s = document.createElement('script');
+  id: string,
+  async: boolean,
+  src: string,
+  onload: (() => void) | null,
+  text: string
+): void {
+  const s = document.createElement('script');
   s.type = 'text/javascript';
   s.id = id;
-  s.key = key;
   s.async = async;
   s.onload = onload;
   s.src = src;
   s.text = text;
   document.getElementsByTagName('head')[0].appendChild(s);
-};
+}
 
-export const scriptRemover = id => {
+export function scriptRemover(id: string): void {
-  let script = document.getElementById(id);
+  const script = document.getElementById(id);
   if (script) {
     script.remove();
   }
-};
+}
 
-export const mathJaxScriptLoader = () =>
+export function mathJaxScriptLoader(): void {
   scriptLoader(
-    'mathjax',
     'mathjax',
     false,
     'https://cdnjs.cloudflare.com/ajax/libs/mathjax/' +
@@ -39,3 +43,4 @@ export const mathJaxScriptLoader = () =>
       document.querySelector('.project-euler')
     ]);`
   );
+}

client/src/utils/to-learn-path.ts

@@ -1,6 +1,15 @@
 import { withPrefix } from 'gatsby';
 
-export default function toLearnPath({ superBlock, block, challenge }) {
+interface ToLearnPathKwargs {
+  superBlock: string;
+  block: string;
+  challenge: string;
+}
+export default function toLearnPath({
+  superBlock,
+  block,
+  challenge
+}: ToLearnPathKwargs): string {
   let path = withPrefix('/learn');
   if (superBlock) path += `/${superBlock}`;
   if (block) path += `/${block}`;