useReducer is a Hook in React that helps manage complex state logic in your application. It is an alternative to useState and is often used together with the Context API to manage the state of your application. useReducer allows you to define and update your state in one place and pass it down to your components. You can use it to handle state transitions, updating multiple state variables together, and managing complex state logic. Here’s an example of how to use useReducer:

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import { useReducer } from 'react';

const initialState = { count: 0 };

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    default:
      throw new Error();
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, initialState);
  return (
    <>
      Count: {state.count}
      <button onClick={() => dispatch({ type: 'increment' })}>+</button>
      <button onClick={() => dispatch({ type: 'decrement' })}>-</button>
    </>
  );
}

In this example, useReducer is used to manage the state of a counter. The reducer function is called each time an action is dispatched and returns the new state of our application. The dispatch function is used to trigger these actions.

The Context API is a built-in feature of React, which allows sharing data between different components without having to pass the data through each level of the component tree manually. It provides a way to pass data through the component tree without the need to pass props down manually at every level. Context specifies a structure for passing information and puts methods to update change within the context. You can learn more about the Context API in the official React documentation: https://reactjs.org/docs/context.html. Here's an example of how to use Context API in React:

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import React, { useContext } from 'react';

const AppContext = React.createContext();

function App() {
  return (
    <AppContext.Provider value="Welcome to SheCodes Community!">
      <MainComponent />
    </AppContext.Provider>
  );
}

function MainComponent() {
  const value = useContext(AppContext);
  return (
    <div>
      <h1>{value}</h1>
      <OtherComponent />
    </div>
  );
}

function OtherComponent() {
  const value = useContext(AppContext);
  return (
    <h2>{value}</h2>
  );
}

In this example, we've created a context called AppContext and set its initial value to Welcome to SheCodes Community!. We then wrapped our MainComponent with AppContext.Provider, providing the value to be used by any child components. We can then access the AppContext value using the useContext hook in MainComponent and OtherComponent. As a result, both components can access the value without being required to pass props down from the App component, even if they are nested at different levels in the component tree.

To use an API with React, you will need to make an HTTP request to the API server endpoint. This can be done using an HTTP library such as axios or the native fetch() API.

Once you have the data from the endpoint, you can use the setState react hook to bind the data to your component's state and render the information to the page.

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// In your component's constructor
constructor(props) {
  super(props);
  this.state = { apiData: [] };
}

// In the function that calls the API
fetchData() {
  Axios.get('http://example.com/api/endpoint')
    .then(response => {
      // Set state with the data returned from the endpoint
      this.setState({ apiData: response.data })
    });
}

// Render the data 
render() {
  return (
    {this.state.apiData.map(data => (
      <span>{data.name}</span>
    ))}
  )
}

Additionally, you can use the React Context API to store the fetched data and bind it to certain components in your application, making it available and reusable in different states of your application.

React 17 was released on April 2021. React 18 fixes some features introduced in React 17 and adds others. The main changes from React 17 are:

• React 18 now supports dynamic imports, which allow code splitting using the [import()] syntax (https://reactjs.org/blog/2020/09/22/introducing-dynamic-imports-in-react-18.html).
• React 17 had several bug fixes related to the JSX transform, the new low-level caching, and more.
• React 18 introduces a few new features including a new context API, an experimental Suspense Hook, and an improved server-side rendering memory utilization.