completed eslint ts setup and fixed eslint issues (#112)

* completed eslint ts setup and fixed eslint issues

* minor change in direction 😄

* upgraded type definitions

* declared custom global variable

* moved global var definition below imports

Author: emin93

README.md

@@ -26,7 +26,7 @@
 ## :arrow_forward: Usage
 
 ### Note on the legacy CLI
-There seems to be quite some confusion about the legacy CLI. This template only works with the new CLI. Make sure you have uninstalled the legacy `react-native-cli` first (`npm uninstall -g react-native-cli`), for the above command to work. If you wish to not use `npx`, you can also install the new CLI globally (`npm i -g @react-native-community/cli` or `yarn global add @react-native-community/cli`).
+There seems to be quite some confusion about the legacy CLI. This template only works with the new CLI. Make sure you have uninstalled the legacy `react-native-cli` first (`npm uninstall -g react-native-cli`), for the below command to work. If you wish to not use `npx`, you can also install the new CLI globally (`npm i -g @react-native-community/cli` or `yarn global add @react-native-community/cli`).
 
 Further information can be found here: https://github.com/react-native-community/cli#about
 

template/App.tsx

@@ -26,8 +26,9 @@ import {
   ReloadInstructions,
 } from 'react-native/Libraries/NewAppScreen';
 
+declare var global: {HermesInternal: null | {}};
+
 const App = () => {
-  const usingHermes = typeof HermesInternal === 'object' && HermesInternal !== null;
   return (
     <>
       <StatusBar barStyle="dark-content" />
@@ -36,7 +37,7 @@ const App = () => {
           contentInsetAdjustmentBehavior="automatic"
           style={styles.scrollView}>
           <Header />
-          {!usingHermes ? null : (
+          {global.HermesInternal == null ? null : (
             <View style={styles.engine}>
               <Text style={styles.footer}>Engine: Hermes</Text>
             </View>

template/_eslintrc.js

@@ -1,4 +1,6 @@
 module.exports = {
   root: true,
   extends: '@react-native-community',
+  parser: '@typescript-eslint/parser',
+  plugins: ['@typescript-eslint'],
 };

template/package.json

@@ -17,9 +17,10 @@
     "@babel/core": "^7.6.2",
     "@babel/runtime": "^7.6.2",
     "@react-native-community/eslint-config": "^0.0.5",
-    "@types/jest": "^24.0.18",
-    "@types/react-native": "^0.60.22",
-    "@types/react-test-renderer": "16.9.0",
+    "@types/jest": "^24.0.24",
+    "@types/react-native": "^0.60.25",
+    "@types/react-test-renderer": "16.9.1",
+    "@typescript-eslint/eslint-plugin": "^2.12.0",
     "@typescript-eslint/parser": "^2.12.0",
     "babel-jest": "^24.9.0",
     "eslint": "^6.5.1",