C questions

`String.prototype.codePointAt` returns an integer representing the UTF-16 code unit at a specified index in a string. It is useful for dealing with Unicode characters. 

const str = '𠮷';
const codePoint = str.codePointAt(0);
console.log(codePoint); // 134071

`String.fromCharCode` returns a string created from the specified sequence of UTF-16 code units. It is used to convert code units to characters. 

const char = String.fromCharCode(65);
console.log(char); // 'A'

`String.prototype.startsWith` checks if a string starts with a specified substring and returns `true` if it does, otherwise `false`. 

const str = 'hello';
console.log(str.startsWith('he')); // true
console.log(str.startsWith('lo')); // false

`String.prototype.endsWith` checks if a string ends with a specified substring and returns `true` if it does, otherwise `false`. 

const str = 'hello';
console.log(str.endsWith('lo')); // true
console.log(str.endsWith('he')); // false

`String.prototype.localeCompare` compares two strings in the current locale and returns a number indicating whether the calling string comes before, after, or is equal to the compared string. 

const str1 = 'apple';
const str2 = 'banana';
const result = str1.localeCompare(str2);
console.log(result); // -1 (str1 is less than str2)

`String.prototype.link` creates an HTML `<a>` element wrapping the string, which is used to create hyperlinks. This method is deprecated and should not be used in modern applications. 

const str = 'Click here';
const linkedStr = str.link('https://example.com');
console.log(linkedStr); // '<a href="https://example.com">Click here</a>'

`String.prototype.fontcolor` returns a string wrapped in HTML `<font>` tags with a specified color. This method is deprecated and should not be used in modern applications. 

const str = 'hello';
const coloredStr = str.fontcolor('red');
console.log(coloredStr); // '<font color="red">hello</font>'

`String.prototype.fontsize` returns a string wrapped in HTML `<font>` tags with a specified size. This method is deprecated and should not be used in modern applications. 

const str = 'hello';
const sizedStr = str.fontsize(7);
console.log(sizedStr); // '<font size="7">hello</font>'

`String.prototype.anchor` creates an HTML `<a>` element wrapping the string with a specified name attribute. This method is deprecated and should not be used in modern applications. 

const str = 'Click here';
const anchoredStr = str.anchor('top');
console.log(anchoredStr); // '<a name="top">Click here</a>'

Common pitfalls with useEffect include missing dependency arrays, leading to infinite loops or stale closures. Ensuring correct dependencies and cleaning up side effects properly with cleanup functions can help avoid these issues and ensure correct behavior.

React DevTools is a browser extension that provides insights into React component hierarchies, state, and props. It aids in debugging by allowing developers to inspect component trees, view hooks and context, and profile performance to identify and resolve issues.

Component lifecycle in functional components is managed using hooks like useEffect, which can perform side effects on mount, update, and unmount. useEffect replaces lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount.

React StrictMode is a development tool that helps identify potential problems in an application by activating additional checks and warnings. It helps catch issues like deprecated APIs, unexpected side effects, and potential problems with components.

Optimizing React's context API involves strategies like using separate contexts for different state slices, memoizing context values, and avoiding deep nesting of contexts. Additionally, consider using useReducer for managing complex context state to minimize unnecessary re-renders.

Techniques for managing side effects in React include using the useEffect hook for handling async operations, leveraging custom hooks to encapsulate side effect logic, and using libraries like Redux Thunk or Redux Saga for complex side effects management.

useContext can simplify global state management by allowing components to access context values directly. However, it can lead to performance issues due to re-renders of all consumers when context values change. For complex state, consider using dedicated state management libraries.

Error boundaries in React are components that catch JavaScript errors anywhere in their child component tree and display a fallback UI. They are implemented using class components with the componentDidCatch method and static getDerivedStateFromError method for error handling.

Strategies for optimizing React component rendering include using React.memo to prevent unnecessary re-renders, memoizing functions with useCallback, splitting components into smaller pieces, and leveraging virtualized lists for large datasets.

React's Concurrent Mode introduces new rendering capabilities that allow React to interrupt and prioritize rendering work, improving user experience by making updates more responsive. It enables features like Suspense and useTransition, leading to smoother and faster UIs.

Authentication in React applications is typically handled through tokens or session management with libraries like React Router for protected routes. Authorization involves controlling access to components based on user roles or permissions, often integrated with backend APIs and state management.

SSR provides faster initial page loads and better SEO but requires server resources and complexity. CSR offers a more interactive user experience and reduces server load but can result in slower initial loads and SEO challenges. The choice depends on the application's needs and goals.

Best practices for structuring a large React application include organizing components into feature-based directories, using hooks and context for state management, adopting a modular approach with code splitting, and maintaining a consistent naming convention and folder structure.

React's reconciliation algorithm uses keys to identify which items in a list have changed, been added, or been removed. Keys help React match elements from previous and next renders, optimizing updates and minimizing re-renders. Proper key usage ensures efficient rendering.

Best practices for managing global state with Redux include organizing state into slices, using action creators and reducers for clarity, employing middleware like Redux Thunk for async actions, and normalizing state to avoid deeply nested structures.

Performance optimization in React applications with large-scale data can be achieved using techniques such as virtualization with libraries like react-window, memoization with useMemo and useCallback, and efficient state management to prevent unnecessary re-renders.