Add ESLint with our standard config (#95)

- Added ESLint + plugins for TypeScript and Prettier.

- Added the standard config + env: {node: true,} to keep TypeScript happy.

- Fixed all the errors that were preventing the app from compiling.

Closes #87.

Author: nina-py

.eslintrc.js

@@ -0,0 +1,54 @@
+module.exports = {
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:@typescript-eslint/recommended',
+    'prettier/@typescript-eslint',
+    'plugin:prettier/recommended',
+  ],
+  plugins: [],
+  rules: {
+    'prettier/prettier': [
+      'error',
+      {
+        useTabs: false, // ＼(￣▽￣)／
+        tabWidth: 2,
+        semi: true,
+        singleQuote: true,
+      },
+    ],
+    // allows unused vars when declared in arguments
+    '@typescript-eslint/no-unused-vars': [
+      'error',
+      { vars: 'all', args: 'none' },
+    ],
+    // disables case checks for class/interface/type
+    '@typescript-eslint/class-name-casing': 0,
+    // disables case checks for properties
+    '@typescript-eslint/camelcase': 0,
+    // allows 'any' typehint
+    '@typescript-eslint/no-explicit-any': 0,
+    // enforces 2 spaces indent
+    indent: [
+      'error',
+      2,
+      {
+        SwitchCase: 1,
+        VariableDeclarator: { var: 2, let: 2, const: 3 },
+        outerIIFEBody: 1,
+        MemberExpression: 1,
+        FunctionDeclaration: { parameters: 1, body: 1 },
+        FunctionExpression: { parameters: 1, body: 1 },
+        CallExpression: { arguments: 1 },
+        ArrayExpression: 1,
+        ObjectExpression: 1,
+        ImportDeclaration: 1,
+        flatTernaryExpressions: false,
+        ignoreComments: false,
+      },
+    ],
+  },
+  env: {
+    node: true,
+  },
+};

package-lock.json

@@ -37,6 +37,11 @@
     ]
   },
   "devDependencies": {
+    "@typescript-eslint/eslint-plugin": "^4.9.1",
+    "@typescript-eslint/parser": "^4.9.1",
+    "eslint": "^7.15.0",
+    "eslint-config-prettier": "^7.0.0",
+    "eslint-plugin-prettier": "^3.2.0",
     "prettier": "^2.2.1"
   }
 }

package.json

@@ -5,7 +5,7 @@ import { MainContentWrapper } from './components/MainContentWrapper/MainContentW
 import { TabNavigation } from './components/TabNavigation/TabNavigation';
 import { Tab } from './components/Tab/Tab';
 
-function App() {
+function App(): JSX.Element {
   return (
     <div>
       <Header />

src/App.tsx

@@ -69,10 +69,13 @@ const useStyles = makeStyles({
   },
 });
 
-export const Header = () => {
+export const Header = (): JSX.Element => {
   const [value, setValue] = React.useState(0);
 
-  const handleChange = (event: React.ChangeEvent<{}>, newValue: number) => {
+  const handleChange = (
+    event: React.ChangeEvent<unknown>,
+    newValue: number
+  ) => {
     setValue(newValue);
   };
 

src/components/Header/Header.tsx

@@ -35,7 +35,10 @@ export const TabNavigation: React.FC<TabNavigationProps> = (props) => {
   /**
    * Callback function required by the props "onChange" of the "Tabs" Material-UI component.
    */
-  const tabChangeHandler = (event: React.ChangeEvent<{}>, newValue: number) => {
+  const tabChangeHandler = (
+    event: React.ChangeEvent<unknown>,
+    newValue: number
+  ) => {
     setValue(newValue);
   };
 

src/components/TabNavigation/TabNavigation.tsx

@@ -25,13 +25,10 @@ type Config = {
   onUpdate?: (registration: ServiceWorkerRegistration) => void;
 };
 
-export function register(config?: Config) {
+export function register(config?: Config): void {
   if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
     // The URL constructor is available in all browsers that support SW.
-    const publicUrl = new URL(
-      process.env.PUBLIC_URL,
-      window.location.href
-    );
+    const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
     if (publicUrl.origin !== window.location.origin) {
       // Our service worker won't work if PUBLIC_URL is on a different origin
       // from what our page is served on. This might happen if a CDN is used to
@@ -65,7 +62,7 @@ export function register(config?: Config) {
 function registerValidSW(swUrl: string, config?: Config) {
   navigator.serviceWorker
     .register(swUrl)
-    .then(registration => {
+    .then((registration) => {
       registration.onupdatefound = () => {
         const installingWorker = registration.installing;
         if (installingWorker == null) {
@@ -101,25 +98,25 @@ function registerValidSW(swUrl: string, config?: Config) {
         };
       };
     })
-    .catch(error => {
+    .catch((error) => {
       console.error('Error during service worker registration:', error);
     });
 }
 
 function checkValidServiceWorker(swUrl: string, config?: Config) {
   // Check if the service worker can be found. If it can't reload the page.
   fetch(swUrl, {
-    headers: { 'Service-Worker': 'script' }
+    headers: { 'Service-Worker': 'script' },
   })
-    .then(response => {
+    .then((response) => {
       // Ensure service worker exists, and that we really are getting a JS file.
       const contentType = response.headers.get('content-type');
       if (
         response.status === 404 ||
         (contentType != null && contentType.indexOf('javascript') === -1)
       ) {
         // No service worker found. Probably a different app. Reload the page.
-        navigator.serviceWorker.ready.then(registration => {
+        navigator.serviceWorker.ready.then((registration) => {
           registration.unregister().then(() => {
             window.location.reload();
           });
@@ -136,13 +133,13 @@ function checkValidServiceWorker(swUrl: string, config?: Config) {
     });
 }
 
-export function unregister() {
+export function unregister(): void {
   if ('serviceWorker' in navigator) {
     navigator.serviceWorker.ready
-      .then(registration => {
+      .then((registration) => {
         registration.unregister();
       })
-      .catch(error => {
+      .catch((error) => {
         console.error(error.message);
       });
   }