adds flow

.flowconfig

@@ -0,0 +1,12 @@
+[libs]
+./node_modules/fbjs/flow/lib
+
+[options]
+esproposal.class_static_fields=enable
+esproposal.class_instance_fields=enable
+
+module.name_mapper='^\(.*\)\.css$' -> 'react-scripts/config/flow/css'
+module.name_mapper='^\(.*\)\.\(jpg\|png\|gif\|eot\|svg\|ttf\|woff\|woff2\|mp4\|webm\)$' -> 'react-scripts/config/flow/file'
+
+suppress_type=$FlowIssue
+suppress_type=$FlowFixMe

package.json

@@ -8,6 +8,7 @@
     "react-dom": "15.4.2"
   },
   "devDependencies": {
+    "flow-bin": "^0.42.0",
     "gh-pages": "^0.12.0",
     "react-scripts": "0.9.1"
   },
@@ -17,6 +18,7 @@
     "test": "react-scripts test --env=jsdom",
     "eject": "react-scripts eject",
     "deploy": "gh-pages -d build",
-    "predeploy": "npm run build"
+    "predeploy": "npm run build",
+    "flow": "flow; test $? -eq 0 -o $? -eq 2"
   }
 }

src/App.js

@@ -1,11 +1,15 @@
+// @flow
 import React, { Component } from 'react';
 import Home from './sites/home/Home';
 import BabelSite from './sites/babelrc/BabelSite';
 import getCurrentSite from './utils/getCurrentSite';
 import './App.css';
 
 class App extends Component {
-  constructor(props) {
+  state: {
+    site: ?string,
+  };
+  constructor(props: {}) {
     super(props);
     this.state = {
       site: getCurrentSite(),
@@ -19,7 +23,7 @@ class App extends Component {
   render() {
     return (
       <div className="App">
-        {this.getTitle === 'Home' &&
+        {this.getTitle() === 'Home' &&
           <h1 className="App__Header">
             {`Config Wizard:`} <strong className="App__Header__Site">{this.getTitle()}</strong>
           </h1>
@@ -34,7 +38,7 @@ class App extends Component {
     );
   }
 
-  getTitle() {
+  getTitle(): string {
     const {site} = this.state;
     if (site === null) {
       return 'Home';
@@ -45,6 +49,7 @@ class App extends Component {
     if (site === 'eslintrc') {
       return '.eslintrc';
     }
+    return '';
   }
 
   renderSite() {

src/utils/getCurrentSite.js

@@ -1,4 +1,5 @@
-const getCurrentSite = () => {
+// @flow
+const getCurrentSite = (): ?string => {
   const url = location.search.slice(1);
   if (url.indexOf('babelrc') === 0) {
     return 'babelrc';

yarn.lock

@@ -2160,6 +2160,10 @@ flatten@^1.0.2:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/flatten/-/flatten-1.0.2.tgz#dae46a9d78fbe25292258cc1e780a41d95c03782"
 
+flow-bin@^0.42.0:
+  version "0.42.0"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.42.0.tgz#05dd754b6b052de7b150f9210e2160746961e3cf"
+
 for-in@^0.1.5:
   version "0.1.6"
   resolved "https://registry.yarnpkg.com/for-in/-/for-in-0.1.6.tgz#c9f96e89bfad18a545af5ec3ed352a1d9e5b4dc8"