function outer() {
    let count = 0;
    return function inner() {
        count++;
        return count;
    };
}
const counter = outer();
console.log(counter()); // 1
console.log(counter()); // 2

const promise = new Promise((resolve, reject) => {
    setTimeout(() => resolve('Done'), 1000);
});
promise
    .then(result => console.log(result)) // Done
    .catch(error => console.error(error))
    .finally(() => console.log('Finished'));

async function fetchData() {
    try {
        const response = await fetch('https://api.example.com/data');
        const data = await response.json();
        return data;
    } catch (error) {
        console.error(error);
    }
}

fetch('https://api.example.com/data', {
    method: 'GET',
    headers: {
        'Content-Type': 'application/json'
    }
})
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error(error));

fetch('https://api.example.com/data', {
    method: 'GET',
    headers: {
        'Content-Type': 'application/json'
    }
});

localStorage.setItem('key', 'value');
console.log(localStorage.getItem('key')); // value
localStorage.removeItem('key');

const socket = new WebSocket('ws://example.com');
socket.onmessage = function(event) {
    console.log(event.data);
};
socket.send('Hello, server!');

// Debounce
function debounce(func, delay) {
    let timeout;
    return function(...args) {
        clearTimeout(timeout);
        timeout = setTimeout(() => func.apply(this, args), delay);
    };
}

// Throttle
function throttle(func, limit) {
    let inThrottle;
    return function(...args) {
        if (!inThrottle) {
            func.apply(this, args);
            inThrottle = true;
            setTimeout(() => inThrottle = false, limit);
        }
    };
}

// React example
const element = <h1>Hello, world!</h1>;
ReactDOM.render(element, document.getElementById('root'));

const MyComponent = React.memo(function MyComponent(props) {
    return <div>{props.value}</div>;
});

const query = `
    {
        user(id: 1) {
            name
            email
        }
    }
`;

fetch('/graphql', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify({ query }),
})
    .then(response => response.json())
    .then(data => console.log(data));

// Redux example
const initialState = { count: 0 };

function reducer(state = initialState, action) {
    switch (action.type) {
        case 'INCREMENT':
            return { count: state.count + 1 };
        default:
            return state;
    }
}

const store = createStore(reducer);
store.dispatch({ type: 'INCREMENT' });
console.log(store.getState()); // { count: 1 }

// Redux example
const initialState = { count: 0 };

function reducer(state = initialState, action) {
    switch (action.type) {
        case 'INCREMENT':
            return { count: state.count + 1 };
        default:
            return state;
    }
}

const store = createStore(reducer);
store.dispatch({ type: 'INCREMENT' });
console.log(store.getState()); // { count: 1 }

const MyContext = React.createContext();

function App() {
    return (
        <MyContext.Provider value="Hello">
            <ChildComponent />
        </MyContext.Provider>
    );
}

function ChildComponent() {
    const value = useContext(MyContext);
    return <div>{value}</div>;
}

// main.js
const worker = new Worker('worker.js');
worker.postMessage('Hello');
worker.onmessage = function(event) {
    console.log(event.data); // Hello from worker
};

// worker.js
onmessage = function(event) {
    console.log(event.data); // Hello
    postMessage('Hello from worker');
};