Update React example to use AC3 and hooks

examples/react/README.md

@@ -10,25 +10,24 @@ This example uses [React](https://reactjs.org/) and [Apollo GraphQL](https://apo
 ## Install dependencies
 
 ```shell
-$ npm install react react-dom react-apollo apollo-boost graphql graphql-tag
+$ npm install react react-dom @apollo/client graphql
 ```
 
 ## Build the component
 
 ```js
-import ApolloClient from 'apollo-boost';
-import React, {Component} from 'react';
+import React, {useState} from 'react';
 import ReactDOM from 'react-dom';
-import gql from 'graphql-tag';
-import {Query} from 'react-apollo';
+import {ApolloClient, InMemoryCache, gql, useQuery} from '@apollo/client';
 
 // initialize a GraphQL client
 const client = new ApolloClient({
+  cache: new InMemoryCache(),
   uri: 'https://countries.trevorblades.com'
 });
 
 // write a GraphQL query that asks for names and codes for all countries
-const GET_COUNTRIES = gql`
+const LIST_COUNTRIES = gql`
   {
     countries {
       name
@@ -37,36 +36,24 @@ const GET_COUNTRIES = gql`
   }
 `;
 
-// create a component that renders an API data-powered select input
-class CountrySelect extends Component {
-  state = {
-    country: 'US'
-  };
+// create a component that renders a select input for coutries
+function CountrySelect() {
+  const [country, setCountry] = useState('US');
+  const {data, loading, error} = useQuery(LIST_COUNTRIES, {client});
 
-  // set the selected country to the new input value
-  onCountryChange = event => {
-    this.setState({country: event.target.value});
-  };
-
-  render() {
-    return (
-      <Query query={GET_COUNTRIES} client={client}>
-        {({loading, error, data}) => {
-          if (loading) return <p>Loading...</p>;
-          if (error) return <p>{error.message}</p>;
-          return (
-            <select value={this.state.country} onChange={this.onCountryChange}>
-              {data.countries.map(country => (
-                <option key={country.code} value={country.code}>
-                  {country.name}
-                </option>
-              ))}
-            </select>
-          );
-        }}
-      </Query>
-    );
+  if (loading || error) {
+    return <p>{error ? error.message : 'Loading...'}</p>;
   }
+
+  return (
+    <select value={country} onChange={event => setCountry(event.target.value)}>
+      {data.countries.map(country => (
+        <option key={country.code} value={country.code}>
+          {country.name}
+        </option>
+      ))}
+    </select>
+  );
 }
 
 ReactDOM.render(<CountrySelect />, document.getElementById('root'));