React Js Get first index of item in array

<!DOCTYPE html>
<html>

<body>
    <div id="app"></div>
    <script type="text/babel" data-presets="env,react">
        const { useState } = React;

function App() {
            const countries = [
                { countryName: "Australia", capitalName: "Canberra" },
                { countryName: "England", capitalName: "London" },
                { countryName: "India", capitalName: "New Delhi" },
            ];
            const [result, setResult] = useState("");

function myFunction() {
                setResult(
                    countries.findIndex((country) => country.countryName === "India")
                );
            }
            return (
                <div className='container'>
                    <h3>React Js find index of object in array by key value</h3>
                    <button onClick={myFunction} className="btn btn-primary">
                        Find Index of India
                    </button>
                    <p>Get index of object in array by key value: {result}</p>
                </div>
            );
        }

ReactDOM.render(<App />, document.getElementById("app"));
    </script>

h3 {
            font-size: 1.5rem;
            margin-bottom: 1rem;
        }

.btn {
            padding: 0.5rem 1rem;
            font-size: 1rem;
            border-radius: 0.25rem;
            background-color: #007bff;
            color: #fff;
            border: none;
            cursor: pointer;
        }

.btn:hover {
            background-color: #0056b3;
        }

p {
            margin-top: 1rem;
        }
    </style>
</body>

</html>

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<!DOCTYPE html>
<html>
​
<head>
    <meta charset="UTF-8" />
    <script src="https://unpkg.com/react@17.0.2/umd/react.development.js"></script>
    <script src="https://unpkg.com/react-dom@17.0.2/umd/react-dom.development.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/@babel/standalone@7.14.6/babel.min.js"></script>
</head>
​
<body>
    <div id="app"></div>
    <script type="text/babel" data-presets="env,react">
        const { useState } = React;
​
        function App() {
            const countries = [
                { countryName: "Australia", capitalName: "Canberra" },
                { countryName: "England", capitalName: "London" },
                { countryName: "India", capitalName: "New Delhi" },
            ];
            const [result, setResult] = useState("");
​
            function myFunction() {
                setResult(
                    countries.findIndex((country) => country.countryName === "India")
                );
            }
            return (
                <div className='container'>
                    <h3>React Js find index of object in array by key value</h3>
                    <button onClick={myFunction} className="btn btn-primary">
                        Find Index of India
                    </button>
                    <p>Get index of object in array by key value: {result}</p>
                </div>
            );
        }
​
        ReactDOM.render(<App />, document.getElementById("app"));
    </script>
​
    <style>
        .container {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            text-align: center;
        }
​
        h3 {
            font-size: 1.5rem;
            margin-bottom: 1rem;
        }
​
        .btn {
            padding: 0.5rem 1rem;
            font-size: 1rem;
            border-radius: 0.25rem;
            background-color: #007bff;
            color: #fff;
            border: none;
            cursor: pointer;
        }
​
        .btn:hover {
            background-color: #0056b3;
        }
​
        p {
            margin-top: 1rem;
        }
    </style>
</body>
​
</html>