Understanding the 'Context' API in React and its Applications

The correct answer to the quiz question is, "To share data across components without prop drilling." This purpose of the Context API in the React.js framework is essential in ensuring that shared state components can be handled more effectively.

The Context API in React

The 'Context' API is a feature in React that allows for a more straightforward way to share state and other data between components without having to manually pass props down multiple levels in the component tree. This process, often referred to as "prop drilling", can result in bloated and hard-to-maintain code. A common scenario where the Context API proves useful is when data needs to be accessible by many components at different nesting levels.

Practical Application of Context API

Suppose you are creating a multi-language website in React. Here, a 'CurrentLanguage' context can be created. The state for the current language can then be housed in a context provider component. Once this is done, any component in the whole application that needs to know the current language can access it quickly.

Here is a simplified version of what the code could look like:

import React, { createContext, useContext, useState } from 'react';

// Create Context object.
const CurrentLanguageContext = createContext();

// Export the Provider component.
export function CurrentLanguageProvider({ children }) {
  const [language, setLanguage] = useState('en');

  // value prop is where we define what values
  // ...that we want to be accessible within the children's components
  return (
    <CurrentLanguageContext.Provider value={{ language, setLanguage }}>
      {children}
    </CurrentLanguageContext.Provider>
  );
}

// Export a custom hook that lets child components easily access the context
export function useCurrentLanguage() {
  return useContext(CurrentLanguageContext);
}

Then, in any component needing access to the current language, you can import the custom hook and use it:

import { useCurrentLanguage } from './CurrentLanguageProvider';

function SomeComponent() {
  const { language } = useCurrentLanguage();
  return <p>The current language is: {language}</p>;
}

Note that as per best practices, you should ensure that you manage the state within your application judiciously. Meaning, it's best to not overuse context as state management for every single piece of state in your application.

In conclusion, the React 'Context' API presents a viable solution to prop drilling and enhances code maintainability and clarity by providing a convenient way to get state and pass down props seamlessly through the component tree.