7 | Hello React Context
8 |
9 |
10 | That's how you use children in React by the way.
11 |
12 |
13 |
14 | With a React useContext Hook instead of Consumer component this
15 | time!
16 |
17 |
;
42 | };
43 |
44 | export default App;
45 |
--------------------------------------------------------------------------------
/src/App.test.js:
--------------------------------------------------------------------------------
1 | import React from 'react';
2 | import ReactDOM from 'react-dom';
3 | import App from './App';
4 |
5 | it('renders without crashing', () => {
6 | const div = document.createElement('div');
7 | ReactDOM.render(, div);
8 | ReactDOM.unmountComponentAtNode(div);
9 | });
10 |
--------------------------------------------------------------------------------
/src/ThemeContext.js:
--------------------------------------------------------------------------------
1 | import React from 'react';
2 |
3 | // could have 'green' as initial value here as well
4 | const ThemeContext = React.createContext(null);
5 |
6 | export default ThemeContext;
7 |
--------------------------------------------------------------------------------
/src/index.js:
--------------------------------------------------------------------------------
1 | import React from 'react';
2 | import ReactDOM from 'react-dom';
3 | import registerServiceWorker from './registerServiceWorker';
4 |
5 | import App from './App';
6 | import ThemeContext from './ThemeContext';
7 |
8 | ReactDOM.render(
9 |
10 |
11 | ,
12 | document.getElementById('root')
13 | );
14 |
15 | registerServiceWorker();
16 |
--------------------------------------------------------------------------------
/src/registerServiceWorker.js:
--------------------------------------------------------------------------------
1 | // In production, we register a service worker to serve assets from local cache.
2 |
3 | // This lets the app load faster on subsequent visits in production, and gives
4 | // it offline capabilities. However, it also means that developers (and users)
5 | // will only see deployed updates on the "N+1" visit to a page, since previously
6 | // cached resources are updated in the background.
7 |
8 | // To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
9 | // This link also includes instructions on opting out of this behavior.
10 |
11 | const isLocalhost = Boolean(
12 | window.location.hostname === 'localhost' ||
13 | // [::1] is the IPv6 localhost address.
14 | window.location.hostname === '[::1]' ||
15 | // 127.0.0.1/8 is considered localhost for IPv4.
16 | window.location.hostname.match(
17 | /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
18 | )
19 | );
20 |
21 | export default function register() {
22 | if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
23 | // The URL constructor is available in all browsers that support SW.
24 | const publicUrl = new URL(process.env.PUBLIC_URL, window.location);
25 | if (publicUrl.origin !== window.location.origin) {
26 | // Our service worker won't work if PUBLIC_URL is on a different origin
27 | // from what our page is served on. This might happen if a CDN is used to
28 | // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
29 | return;
30 | }
31 |
32 | window.addEventListener('load', () => {
33 | const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
34 |
35 | if (!isLocalhost) {
36 | // Is not local host. Just register service worker
37 | registerValidSW(swUrl);
38 | } else {
39 | // This is running on localhost. Lets check if a service worker still exists or not.
40 | checkValidServiceWorker(swUrl);
41 | }
42 | });
43 | }
44 | }
45 |
46 | function registerValidSW(swUrl) {
47 | navigator.serviceWorker
48 | .register(swUrl)
49 | .then(registration => {
50 | registration.onupdatefound = () => {
51 | const installingWorker = registration.installing;
52 | installingWorker.onstatechange = () => {
53 | if (installingWorker.state === 'installed') {
54 | if (navigator.serviceWorker.controller) {
55 | // At this point, the old content will have been purged and
56 | // the fresh content will have been added to the cache.
57 | // It's the perfect time to display a "New content is
58 | // available; please refresh." message in your web app.
59 | console.log('New content is available; please refresh.');
60 | } else {
61 | // At this point, everything has been precached.
62 | // It's the perfect time to display a
63 | // "Content is cached for offline use." message.
64 | console.log('Content is cached for offline use.');
65 | }
66 | }
67 | };
68 | };
69 | })
70 | .catch(error => {
71 | console.error('Error during service worker registration:', error);
72 | });
73 | }
74 |
75 | function checkValidServiceWorker(swUrl) {
76 | // Check if the service worker can be found. If it can't reload the page.
77 | fetch(swUrl)
78 | .then(response => {
79 | // Ensure service worker exists, and that we really are getting a JS file.
80 | if (
81 | response.status === 404 ||
82 | response.headers.get('content-type').indexOf('javascript') === -1
83 | ) {
84 | // No service worker found. Probably a different app. Reload the page.
85 | navigator.serviceWorker.ready.then(registration => {
86 | registration.unregister().then(() => {
87 | window.location.reload();
88 | });
89 | });
90 | } else {
91 | // Service worker found. Proceed as normal.
92 | registerValidSW(swUrl);
93 | }
94 | })
95 | .catch(() => {
96 | console.log(
97 | 'No internet connection found. App is running in offline mode.'
98 | );
99 | });
100 | }
101 |
102 | export function unregister() {
103 | if ('serviceWorker' in navigator) {
104 | navigator.serviceWorker.ready.then(registration => {
105 | registration.unregister();
106 | });
107 | }
108 | }
109 |
--------------------------------------------------------------------------------