);
+ }
+}
+
+export default Clock;
\ No newline at end of file
diff --git a/counter/src/Counter.js b/counter/src/Counter.js
new file mode 100644
index 000000000..5d2b0fb5e
--- /dev/null
+++ b/counter/src/Counter.js
@@ -0,0 +1,31 @@
+import React, {Component} from "react";
+
+class Counter extends Component {
+ state = {
+ num: this.props.number
+ };
+
+ //setState를 해야만 화면이 갱신된다.
+ //this, binding에 대하여 javascript스터디들 해보자. 이 이유 때문에 () => 를 사용한다.
+ handleInc = () => {
+ this.setState({
+ num: this.state.num + 1
+ });
+ };
+
+ render() {
+ //this.props.number = 10; //props는 변경이 불가능하다.
+ //this.handeInc()를 하면 첫 랜더링에서 함수가 자동으로 호출된다. 이후에 setState하면서 계속 화면 갱신.. 무한루프로 계속갱신 --> 에러
+ return
+ counter
+
{this.props.number}
+
{this.state.num}
+
+
+
+
+
;
+ }
+}
+
+export default Counter;
\ No newline at end of file
diff --git a/counter/src/index.css b/counter/src/index.css
new file mode 100644
index 000000000..ec2585e8c
--- /dev/null
+++ b/counter/src/index.css
@@ -0,0 +1,13 @@
+body {
+ margin: 0;
+ font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
+ 'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
+ sans-serif;
+ -webkit-font-smoothing: antialiased;
+ -moz-osx-font-smoothing: grayscale;
+}
+
+code {
+ font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
+ monospace;
+}
diff --git a/counter/src/index.js b/counter/src/index.js
new file mode 100644
index 000000000..87d1be551
--- /dev/null
+++ b/counter/src/index.js
@@ -0,0 +1,12 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+import './index.css';
+import App from './App';
+import * as serviceWorker from './serviceWorker';
+
+ReactDOM.render(, document.getElementById('root'));
+
+// If you want your app to work offline and load faster, you can change
+// unregister() to register() below. Note this comes with some pitfalls.
+// Learn more about service workers: https://bit.ly/CRA-PWA
+serviceWorker.unregister();
diff --git a/counter/src/logo.svg b/counter/src/logo.svg
new file mode 100644
index 000000000..6b60c1042
--- /dev/null
+++ b/counter/src/logo.svg
@@ -0,0 +1,7 @@
+
diff --git a/counter/src/serviceWorker.js b/counter/src/serviceWorker.js
new file mode 100644
index 000000000..8703ddb7e
--- /dev/null
+++ b/counter/src/serviceWorker.js
@@ -0,0 +1,137 @@
+// This optional code is used to register a service worker.
+// register() is not called by default.
+
+// This lets the app load faster on subsequent visits in production, and gives
+// it offline capabilities. However, it also means that developers (and users)
+// will only see deployed updates on subsequent visits to a page, after all the
+// existing tabs open on the page have been closed, since previously cached
+// resources are updated in the background.
+
+// To learn more about the benefits of this model and instructions on how to
+// opt-in, read https://bit.ly/CRA-PWA
+
+const isLocalhost = Boolean(
+ window.location.hostname === 'localhost' ||
+ // [::1] is the IPv6 localhost address.
+ window.location.hostname === '[::1]' ||
+ // 127.0.0.0/8 are considered localhost for IPv4.
+ window.location.hostname.match(
+ /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
+ )
+);
+
+export function register(config) {
+ if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
+ // The URL constructor is available in all browsers that support SW.
+ const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
+ if (publicUrl.origin !== window.location.origin) {
+ // Our service worker won't work if PUBLIC_URL is on a different origin
+ // from what our page is served on. This might happen if a CDN is used to
+ // serve assets; see https://github.com/facebook/create-react-app/issues/2374
+ return;
+ }
+
+ window.addEventListener('load', () => {
+ const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
+
+ if (isLocalhost) {
+ // This is running on localhost. Let's check if a service worker still exists or not.
+ checkValidServiceWorker(swUrl, config);
+
+ // Add some additional logging to localhost, pointing developers to the
+ // service worker/PWA documentation.
+ navigator.serviceWorker.ready.then(() => {
+ console.log(
+ 'This web app is being served cache-first by a service ' +
+ 'worker. To learn more, visit https://bit.ly/CRA-PWA'
+ );
+ });
+ } else {
+ // Is not localhost. Just register service worker
+ registerValidSW(swUrl, config);
+ }
+ });
+ }
+}
+
+function registerValidSW(swUrl, config) {
+ navigator.serviceWorker
+ .register(swUrl)
+ .then(registration => {
+ registration.onupdatefound = () => {
+ const installingWorker = registration.installing;
+ if (installingWorker == null) {
+ return;
+ }
+ installingWorker.onstatechange = () => {
+ if (installingWorker.state === 'installed') {
+ if (navigator.serviceWorker.controller) {
+ // At this point, the updated precached content has been fetched,
+ // but the previous service worker will still serve the older
+ // content until all client tabs are closed.
+ console.log(
+ 'New content is available and will be used when all ' +
+ 'tabs for this page are closed. See https://bit.ly/CRA-PWA.'
+ );
+
+ // Execute callback
+ if (config && config.onUpdate) {
+ config.onUpdate(registration);
+ }
+ } else {
+ // At this point, everything has been precached.
+ // It's the perfect time to display a
+ // "Content is cached for offline use." message.
+ console.log('Content is cached for offline use.');
+
+ // Execute callback
+ if (config && config.onSuccess) {
+ config.onSuccess(registration);
+ }
+ }
+ }
+ };
+ };
+ })
+ .catch(error => {
+ console.error('Error during service worker registration:', error);
+ });
+}
+
+function checkValidServiceWorker(swUrl, config) {
+ // Check if the service worker can be found. If it can't reload the page.
+ fetch(swUrl, {
+ headers: { 'Service-Worker': 'script' }
+ })
+ .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 => {
+ registration.unregister().then(() => {
+ window.location.reload();
+ });
+ });
+ } else {
+ // Service worker found. Proceed as normal.
+ registerValidSW(swUrl, config);
+ }
+ })
+ .catch(() => {
+ console.log(
+ 'No internet connection found. App is running in offline mode.'
+ );
+ });
+}
+
+export function unregister() {
+ if ('serviceWorker' in navigator) {
+ navigator.serviceWorker.ready.then(registration => {
+ registration.unregister();
+ });
+ }
+}
diff --git a/counter/src/setupTests.js b/counter/src/setupTests.js
new file mode 100644
index 000000000..74b1a275a
--- /dev/null
+++ b/counter/src/setupTests.js
@@ -0,0 +1,5 @@
+// jest-dom adds custom jest matchers for asserting on DOM nodes.
+// allows you to do things like:
+// expect(element).toHaveTextContent(/react/i)
+// learn more: https://github.com/testing-library/jest-dom
+import '@testing-library/jest-dom/extend-expect';