100 Essential React Interview Questions

1. What is React and why is it used?

React is an open-source, front-end JavaScript library for building user interfaces, that focuses on reusable components and virtual DOM for performance.

Core Concepts

Virtual DOM

React's Virtual DOM is a lightweight in-memory representation of the actual DOM elements. When changes occur, React compares the current Virtual DOM with a shadow copy and efficiently updates only the changed portions in the real DOM.

This mechanism significantly reduces expensive direct DOM manipulations, resulting in improved performance and responsiveness in web applications.

Components

React Components encapsulate both the visual and the corresponding logic. They can be either classes or pure functions. This modular architecture and the ability to nest and reuse components make React a powerful UI toolkit.

Components are broken down into two main types:

1. Class Components: These are ES6 classes that can hold state and offer lifecycle methods.
2. Functional Components: Primarily plain JavaScript functions: until the advent of "hooks," they couldn't maintain states.

Key changes, starting from React 16.8:

• Introduction of new hooks API expanded state-management to functional components
• Popular hooks include useState for state management and useEffect for lifecycle management.

Beyond this foundational structure, hooks offer extensive state, lifecycle, and context APIs, making functional components powerful building blocks.

Unidirectional Data-flow

React mandates a one-way data flow, empowering developers to understand and manage data propagation more effectively. This simplifies tracking, debugging, and validating data changes across the application.

While sibling components can communicate indirectly through shared parent components, direct communication among sibling components is typically discouraged.

JSX: Syntactic Sugar

JSX empowers developers by offering a more intuitive, HTML-like syntax for embedding JavaScript expressions. This marriage of UI and logic not only renders extensive possibilities but also promotes code organization and readability.

Why use React?

Declarative Programming Paradigm

React enables a declarative style of programming: developers define the interface's desired state, and React ensures the DOM reflects that state. This approach is more intuitive and helps in designing clear, maintainable code.

Strong Community Backing and Ecosystem

React has been gaining momentum with an enthusiastic community regularly contributing new solutions, updates, and robust third-party libraries. The supportive ecosystem extends to comprehensive toolsets for better development and debugging (like React DevTools).

Reusability and Composability

React's architecture is built on reusable components, fostering modular, consistent UI elements and logic that can be redeployed across projects or shared with others.

Performance Optimization

The Virtual DOM serves as a powerful performance amplifier, and features like providing keys to iterated lists ensure efficient and targeted DOM updates. React is also capable of server-side rendering, bolstering app speed and SEO-friendliness.

Effective Data Management

For application-wide state management, React provides Context API and libraries like Redux. Meanwhile, local state management with hooks like useState streamlines state handling within components.

Code Example: Functional vs Class-Based Components

Here is the React code:

// Functional Component with useState hook
import React, { useState } from 'react';

export default function Button() {
  const [count, setCount] = useState(0);
  return (
    <button onClick={() => setCount(count + 1)}>
      Clicked {count} times
    </button>
  );
}

// Class-based Component
import React, { Component } from 'react';

export default class Button extends Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  render() {
    return (
      <button onClick={() => this.setState({ count: this.state.count + 1 })}>
        Clicked {this.state.count} times
      </button>
    );
  }
}

2. How is React different from Angular or Vue?

When comparing React, Angular, and Vue.js, a few key differentiators stand out.

Core Philosophy

• React: Focuses on UI components. You need other libraries for state management, routing, etc.
• Angular: Provides a more comprehensive solution out of the box, often called "batteries included."
• Vue.js: A good balance of providing core libraries and flexibility for integration with third-party tools.

Learning Curve

• React: Initially simpler to learn due to its focused nature, but can become complex as you add more external libraries.
• Angular: Steeper learning curve because of its complete ecosystem, including modules, services, and complex directives.
• Vue.js: Known for its gentle learning curve and clear, concise documentation.

Community and Ecosystem

• React: Enjoys an enormous community, and users can pick and choose from a vast array of third-party libraries to complement its core features.
• Angular: Boasts a comprehensive ecosystem that's well-managed by its developers and is known for its enterprise support.
• Vue.js: While the newest of these frameworks, it has been growing rapidly, with a dedicated team and a flourishing community.

Performance

• React: Focuses on efficient rendering and offers built-in tools for performance optimization.
• Angular: Optimizes performance through features like Ahead-Of-Time (AOT) compilation and Zone.js, which prevents unnecessary digest cycles.
• Vue.js: Also optimized for performance, with a small bundle size and features like lazy-loading components.

Official State Management

• React: Employs component state (with setState) and also external state management libraries like Redux, MobX, and the newer Context API.
• Angular: Primarily uses services and RxJS for more structured reactive state management.
• Vue.js: Offers Vuex, a state management pattern and library dedicated to Vue applications.

Language Support

• React: Developed with JavaScript and its supersets (JSX and TypeScript) in mind.
• Angular: Primarily designed for TypeScript but supports JavaScript and Dart as well.
• Vue.js: Offers support for both JavaScript and TypeScript.

Templating Approach

• React: Utilizes JSX, which combines HTML and JS within JavaScript files. It offers a more concise approach and closely intertwines HTML with JS logic.
• Angular: Has a complete separation of concerns with TypeScript, HTML, and CSS in separate files.
• Vue.js: Allows for both single-file components (SFCs) that encapsulate HTML, JavaScript, and CSS, as well as the traditional trio of separate files.

Language Server Support

• React: Known for limited tooling support due to runtime-oriented nature, but effective tooling is available for TypeScript and Flow.
• Angular: Offers full TypeScript support with features like auto-completion, refactoring, and more, thanks to its built-in language service.
• Vue.js: Supports comprehensive programming features, including type verification, integrated debugging, and intelligent code suggestions.

3. What is a React component?

A React component represents a modular, reusable piece of the user interface. It can encapsulate both visual elements (rendered in the Virtual DOM) and application logic. React components come in two primary forms: function components and class components.

Function vs. Class Components

• Function Components: These are stateless, simpler to read, and ideally used for small, specialized UI elements known as 'dumb' components. They are pure functions, perceptually faster because of fewer checks.

• Class Components: These can maintain state and expose more advanced features like lifecycle methods. However, the introduction of hooks to function components in React 16.8 technically made state management possible without classes.

JSX and render()

React components generally use JSX (an XML-like syntax) to describe the UI and a render() method to define the visual makeup.

• JSX: This "syntactic sugar" streamlines component building. It is converted into standard JavaScript calls. Babel is often used to compile this code.
• render(): Required for class components, it tells React what the component's output should be when rendered.

Structural Coherence

Components in React link together, forming a tree structure. A root component is the entry point, and from there, it houses other components.

Data Flow

React follows a unidirectional data flow. This means data moves from the top of the component tree (parent) down to leaves (children) through component props. Changes are signaled back up the tree via callbacks.

State and Props

Both function and class components can receive data via two main routes:

• Props: Short for properties, these are akin to function arguments and are immutable. They're the mechanism for parent-child data transfer.
• State: This is functionally the component's "memory" and is mutable. Components keep track of their state and re-render upon state change.

Lifecycle Operations

Class components support a series of lifecycle methods. These can be used to run code at specific points in the component's lifecycle, such as upon mounting (creation), updating, or unmounting (removal).

Custom classes and the lifecycle methods within were the primary mechanism for side effects earlier in React. While class-based components aren't as central to the framework with the advent of hooks, they're still relevant and in use, especially when using versions < 16.8.1 and realizing the components' lifecycle patterns in codebases.

4. How do you create a component in React?

Creating a React component involves defining its structure, behavior, and sometimes lifecycle methods for dynamic updates. Components can be functional or class-based.

Code Example

Here's a Class-based component:

import React, { Component } from 'react';

class Greeting extends Component {
  render() {
    return <h1>Hello, {this.props.name}!</h1>;
  }
}

And here's a Functional one:

import React from 'react';

const Greeting = ({ name }) => <h1>Hello, {name}!</h1>;

Both examples showcase a basic greeting component that takes in a prop name and displays a greeting message.

Linters and JSX

Many modern text editors and IDEs support JSX and JavaScript syntax, especially when integrated with linters like ESLint. This setup provides real-time feedback on errors and formatting issues.

Code Styling with AirBNB and Prettier

It's common to see code bases following the Airbnb style guide, often coupled with Prettier for consistent and automated code formatting.

In the context of component creation, these standards can dictate whether to use single or double quotes for JSX attributes and the method for defining components.

Key Takeaways

• JSX offers a natural, HTML-like syntax for building components in React.
• Components can be function-based or class-based.
• Use modern editing tools and linters for improved code consistency and spotting potential issues in real-time.

5. What is JSX and why do we use it in React?

JSX is a powerful JavaScript Extension that enables the seamless integration of HTML-like structures within React. Notably, it allows for a more intuitive component declaration and enhanced developer productivity.

Key Features

• Readable Syntax: Familiar HTML tags make parsing code and debugging simpler.

• Component Embedding: JSX supports direct embedding of components, which enhances modularity.

• Automatic Babel Conversion: Behind the scenes, JSX and its HTML-like tags are transpiled into JavaScript for browser compatibility.

Benefits of Using JSX

• Code Compactness: JSX helps avoid lengthy React.createElement calls.

• Type Safety: Modern IDEs provide extensive support for type checking and autocompletion with JSX.

• Compile-Time Optimizations: JSX allows for compile-time optimizations, enhancing app performance.

• Enable Optional Syntax Checks: For those developing in TypeScript, JSX enables Syntax Checks to ensure code quality.

Code Example: JSX and Its Transpiled Output

Here is the JSX code

// JSX
const element = <h1>Hello, World!</h1>;

Here is the equivalent JS code transpiled by Babel:

// Transpiled JS
const element = React.createElement('h1', null, 'Hello, World!');

Why Use JSX?

• Concise Syntax: JSX provides a succinct, declarative approach to building UIs.

• Improved Readability: Its obvious resemblance to HTML promotes code clarity and reduces cognitive load.

• Static Type Checking: When used with TypeScript or Flow, JSX brings the benefits of type safety, reducing the probability of runtime errors.

• Development Efficiency: By simplifying UI code and providing helpful developer features, JSX accelerates the development process.

• React Ecosystem Integration: JSX is the preferred way to write components across the React ecosystem, fostering community best practices.
  
  

6. Can you explain the virtual DOM in React?

The Virtual DOM is a key concept in React, responsible for its high performance. It efficiently manages the DOM setup, minimizes updates, and then syncs them to the actual DOM tree.

How the Virtual DOM Works

1. Initial Rendering: When the application starts, React creates a simplified in-memory representation of the DOM, called the Virtual DOM.

2. Tree Comparison: During each state change, React builds a new Virtual DOM representation. It then compares this updated representation against the previous one to identify what has changed. This process is often called "reconciliation".

3. Selective Rendering: React determines the most minimal set of changes needed to keep the Virtual DOM in sync with the actual DOM. This approach, known as "reconciliation", is a performance booster as it reduces unnecessary updates.

4. Batched Updates: React performs the actual DOM updates in a batch, typically during the next animation frame or when no more updates are being made. This batching leads to optimized DOM operations, further enhancing performance.

5. One-Way Sync: After the in-memory Virtual DOM and the actual DOM have been reconciled and the necessary updates identified, React syncs these changes in a one-way process, from the Virtual DOM to the actual DOM. This approach helps prevent unnecessary visual glitches and performance hits.

6. Asynchronous Handling: React schedules state changes, ensuring performance by bundling multiple changes that can be processed together. This aids in avoiding unnecessary Virtual DOM updates and ensures efficient tree comparisons.

7. Preventing Direct DOM Manipulation: React applications typically avoid manual DOM manipulation. Instead, all changes are made through React, which then uses its Virtual DOM mechanism to batch and apply these changes to the actual DOM.

8. Support for Cross-Platform Environments: The Virtual DOM gives sturdy cross-platform capabilities, enabling consistent and optimized performance irrespective of the underlying operating system or hardware.

React's Virtual DOM is primarily powered through its component architecture and extensive use of JavaScript, fundamentally changing how web applications are built and perform. Its virtuous efficiency is a testament to React's prowess as a leading front-end framework and contributes to the seamless user experiences React applications are known for providing.

7. What are the differences between a class component and a functional component?

Let's look at the various aspects and differences between Class Components and Functional Components.

Core Distinctions

Class Components:

• Utilize the class keyword for component definition.
• Can have state management.
• Allow lifecycle methods.
• Are typically verbose.

Functional Components:

• Defined using ES6 functions.
• Lack inherent state or lifecycle management.
• Primarily used for UI representation.
• Introduced Hooks in React 16.8 for state and lifecycle control.

Detail Evaluation

Code Structure

Class Components:

• Consists of a render() method.
• Can incorporate other methods for state updates and lifecycle management.

Functional Components:

• Evolved with introduction of React hooks.
• useState() and useEffect() for state and lifecycle management respectively.

Purpose and Use-Cases

Class Components:

• Suitable for more complex components.
• May be necessary in older codebases.
• Gradually being replaced by hooks and functional components.

Functional Components:

• Focused on UI without managing state.
• Introduced hooks to handle state and lifecycle methods.

Editable State

Class Components:

• Use this.state and this.setState() to manage state.
• Useful when state contains complex data types.

Functional Components:

• Implement useState hook to enable state management in functions.
• Introduced for state management in functional components, simplifying state handling.

Lifecycle Methods

Class Components:

• Offer a wide range of lifecycle methods.
• Example methods include componentDidMount and componentWillUnmount.

Functional Components:

• Limited lifecycle management before the introduction of hooks.
• Use useEffect() to handle actions based on state and props changes.

Context API and Redux Usage

Class Components:

• Can easily be paired with both Context API and Redux.
• Typically used with render props.

Functional Components:

• With hooks like useContext, have become proficient in handling shared state.
• Can now be seamlessly integrated with newer global state management libraries like Redux.

Adoption and Transition

• Initial React versions were heavily reliant on class components.
• Hooks' introduction in React 16.8 facilitated the shift towards fully functional components.
• While gradual migration from class to functional is encouraged because of performance benefits, both paradigms can still coexist.

Key Takeaways

• Class Components:

  • Traditional class-based components.
  • Prefers this context.
  • Houses extensive lifecycle methods.
  • Stands as a more elaborate and structured option.

• Functional Components:

  • Evolved to include hooks for state management.
  • Favored for their simplicity and ease of reusability.
  • Perfect for simpler, stateless components.

8. How do you handle events in React?

React simplifies the process of managing and handling events through its use of synthetic events.

Handling Events in React

Synthetic Events

React abstracts browser events into what are known as synthetic events. This ensures a consistent interface across different browsers.

Event Subscription

• When handling events, React behaves consistently across all elements, not just form elements.

• React events use camelCase, unlike HTML, which is helpful for both consistency and avoiding reserved words in JavaScript.

• Use boolean attributes in JSX for default browser events.

Special Event Handling

React provides special interfaces for certain types of events: input components benefit from the value attribute, while media components make use of src or other similar attributes specific to their type.

Code Example: Event Handling

Here is the JavaScript code:

import React from 'react';

class Form extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: '' };

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({ value: event.target.value });
  }

  handleSubmit(event) {
    alert('A name was submitted: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" value={this.state.value} onChange={this.handleChange} />
        </label>
        <input type="submit" value="Submit" />
      </form>
    );
  }
}

9. What are state and props in React?

In React, props and state are both used to propagate and manage data. However, they have different roles and management patterns.

Role & Life Cycle

• Props (short for "properties") are used to pass data from a parent component to a child one. Once passed, props in the child component are read-only and can't be directly modified by the child.

• State is used to manage data within a component, and is mutable. Any changes to state values trigger a component re-render.

When to Use

• Props are for data that does not change within the component and is provided by a parent.
• State is for data that does change within the component and is managed by that component itself.

Management

• When a component receives new props, React will merge them with any existing state. However, it won't override state values unless you explicitly set them.

• Since React re-renders the entire component when you update state, it's important to be efficient in state management. Tools like useMemo or shouldComponentUpdate can help optimize re-renders.

Unifying with Hooks

• The useState hook (along with other hooks like useEffect) allows functional components to manage state, bringing them closer in capability to class components.

• Prior to the introduction of hooks in React 16.8, state was the exclusive domain of class components. But now, both state and its associated lifecycle hooks belong to functional components as well.

Code Example: State and Props Management

Here is the JavaScript code:

import React, { useState } from 'react';

// Button Component
const Button = ({ text, color }) => {
  return <button style={{background: color}}>{text}</button>;
};

// ColorPicker Component
const ColorPicker = () => {
  const [color, setColor] = useState('blue');

  const changeColor = (newColor) => {
    setColor(newColor);
  };

  return (
    <div>
      <Button text="Red" color="red" onClick={() => changeColor('red')} />
      <Button text="Blue" color="blue" onClick={() => changeColor('blue')} />
      <Button text="Green" color="green" onClick={() => changeColor('green')} />
    </div>
  );
};

// App Component
const App = () => {
  return <ColorPicker />;
};

10. How do you pass data between components in React?

Data propagation in React components primarily relies on two mechanisms:

• Props: For unidirectional data flow, parent components pass data to their children via props.

• Callback Functions: Data moves up the tree when children invoke specific functions passed down from their parents.

Let's have a look at the best-practices for these two mechanisms.

Using Props

• Role: Primarily used for one-way data flow. The parent furnishes the child with props that the child component can neither alter nor reassign.

• Best Practices:

  • Leverage props for read-only data in child components.
  • Rerender the child component, if necessary, when the prop values change.

• Code Example: Read-Only Checkbox:

Your task is to write the full code for the React Application to demonstrate passing data to child components using props.

Children Built With Props

In this code example, App maintains the optionSelected state that it shares with the DropDown and SelectedOption components. DropDown uses the optionSelected state to determine which option was picked, shared with SelectedOption to display it.

// src/components/DropDown.tsx
interface DropDownProps {
  options: string[]
}

const DropDown: React.FC<DropDownProps> = ({ options }) => {
  const [selected, setSelected] = React.useState(0);

  return (
    <div>
      <div>Options:</div>
      {options.map((opt, index) => (
        <button key={index} onClick={() => setSelected(index)}>{opt}</button>
      )}
      <SelectedOption option={options[selected]} />
    </div>
  );
};

// src/components/SelectedOption.tsx
interface SelectedOptionProps {
  option: string
}

const SelectedOption: React.FC<SelectedOptionProps> = ({ option }) => {
  return <div>You selected: {option}</div>;
};

// src/App.tsx
const App: React.FC = () => {
  const options = ['Apple', 'Banana', 'Cherry'];
  return <DropDown options={options} />;
};

export default App;

11. What is a stateful component?

Stateful components in React are fueled by internal states, allowing them to adapt to user interactions and data changes.

By invoking this.setState(), components update their state, triggering a re-render and ensuring the UI and state are in sync.

When to Use

• Dynamic Interactions: For components that require dynamic updates, such as a counter that increments on every click.

• User Input Handling: Useful for capturing and validating user inputs in forms.

• Data Fetching: To manage and display data obtained from API calls.

Code Example: Stateful Component

Here is the JavaScript code:

import React, { Component } from 'react';

class ClickCounter extends Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  handleIncrement = () => {
    this.setState(prevState => ({ count: prevState.count + 1 }));
  }

  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
        <button onClick={this.handleIncrement}>Increment</button>
      </div>
    );
  }
}

export default ClickCounter;

12. Can you explain how useState works?

useState is a built-in React Hook that empowers components to preserve stateful values. It amalgamates a stateful value with a state-modifying function, enabling direct manipulation.

Hooks are utility functions that enable you to manage state, side effects, and other React features in function components.

Core Components of useState

1. Stateful Value: The first element in the tuple returned by useState carries the current state, like any other state in React.

2. Setter Function: The second element is a function that determines the state's new value. Upon invocation, it imparts this new state to the component, just as setState does in classes.

Given value as the stateful value and setValue as the setter function, calling setValue(newValue) will alter value to newValue.

Behavioral Traits of useState

• Lazy Initialization: If the stateful value necessitates a computationally intensive or time-consuming setup, employing useState ensures that this setup occurs exclusively when the component is first rendered rather than on every update.

• Referential Integrity: If you employ the useState Hook at distinct spots within a component or even dissimilar components, React guarantees that each endeavor manages its unique state underlying value, akin to using this.state in classes.

Code Example: useState

Here is the React Component:

import React, { useState } from 'react';

const Counter = () => {
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
};

13. How do you update the state of a parent component from a child component?

React encourages unidirectional data flow, primarily passing data from parent to child. However, occasional need arises to update parent state from a child component. This can be facilitated using specific patterns and techniques.

Primary Methods

1. Props Callback: Pass a function onStateChange as a prop which the child can call to update parent state.

2. Context API: Use Context to make state accessible and modifiable from descendant components.

Advanced Techniques

1. UseRef and ForwardRef: Utilize useRef and forwardRef to get a reference to a child component, allowing you to directly manipulate its properties.

2. Global State Management: Implement a global state management solution like Redux or MobX if state changes are pervasive.

3. Data Services: Use a service to manage shared state, which can be updated and read by different components.

Code Example: State Management

Here is the React Component:

// App.js - Parent component
import React, { useState } from 'react';
import Child from './Child';

function Parent() {
  const [state, setState] = useState('');

  const updateState = (newState) => {
    setState(newState);
  };

  return <Child updateParentState={updateState} />;
}

// Child.js - Child component
import React from 'react';

function Child({ updateParentState }) {
  const handleClick = () => {
    updateParentState('New state from child!');
  };

  return <button onClick={handleClick}>Update Parent</button>;
}

In this example, the Parent component maintains the state, which is updated via the function updateState passed as a prop to Child. When a button inside Child is clicked, the updateParentState function updates the parent state.

14. What is lifting state up in React?

Lifting State Up in React entails managing state in parent components to propagate it to multiple children, typically to ensure synchronization or data flow.

Why Use Lifting State Up?

• Consistent Data: Prevents inconsistencies in related data scattered across components.
• Easier Data Modifications: Minimizes complexity when updating shared data, especially with complex data structures or numerous children.

Core Mechanism: Props

React components communicate using props, where child components receive data from parents. During lifting state up, the parent maintains the state and passes down relevant data as props.

Lifting State Up in Code

Here is the React code:

Parent Component: RectangleAreaCalculator

class RectangleAreaCalculator extends React.Component {
  constructor(props) {
    super(props);
    this.state = { width: 0, height: 0 };
  }

  render() {
    return (
      <div>
        <ShapeInput
          type="number"
          label="Width"
          value={this.state.width}
          onChange={(e) => this.setState({ width: e.target.value })}
        />
        <ShapeInput
          type="number"
          label="Height"
          value={this.state.height}
          onChange={(e) => this.setState({ height: e.target.value })}
        />
        <ShapeArea area={this.state.width * this.state.height} />
      </div>
    );
  }
}

Child Components: ShapeInput and ShapeArea

const ShapeInput = ({ type, label, value, onChange }) => (
  <div>
    <label>{label}</label>
    <input type={type} value={value} onChange={onChange} />
  </div>
);

const ShapeArea = ({ area }) => <div>Area: {area}</div>;

In this example, the RectangleAreaCalculator maintains the width and height state and passes them as props to the ShapeInput components. The ShapeArea component calculates the area and receives width and height as props, keeping its state logic-free.

Advantages

• Single Source of Truth: Shared data lives in the parent, reducing complexities stemming from data redundancy or inconsistencies.
• Predictable Data Flow: Changes to the data layer (parent) trigger updates to all its children. This helps in maintaining the coding standards and data integrity.

Most Common Implementations

• Form State: Centralizes form data management in one place, simplifying form submissions or data validation.
• Shared Logic: Multiple components using the same data or functionality can benefit from centralized state management.

When It's Overkill

For small-scale apps or in situations with data that lacks a clear source of "truth", the technique might introduce unnecessary complexity.

Aiming for a balance between centralized and localized state management is key, and React provides tools like useContext and useState that cater to both requirements.

15. When do you use Redux or Context API for state management?

Redux and the Context API serve as tools for managing state in large React applications. Here are situations which might call for one or the other, or even both:

Advantages of Redux

1. Full App Coverage: Redux operates on a global state, enabling consistent app behavior and simplifying state transitions across components.

2. Predictable State Changes: Changes in Redux follow a strict flow, optimizing teamwork and troubleshooting.

3. Time Travel: Redux devtools allow for easy time travel, aiding in bug detection and state history visualization.

4. Performance Optimization: With its selective rendering feature, connect from react-redux ensures only the required components are updated, thus mitigating wasteful renders.

5. Optimal for Bigger Apps:

• Reduces the need for props drilling.
• Offers a centralized point for state changes.

When to Pick Redux

• Large Apps with Complex State: Ideal for apps with intensive state requirements and a multitude of components.

• Frequent Inter-Component Communications: When different sections of your application need to exchange data often, a central store, such as Redux, can streamline this process.

Advantages of Context API

1. Simplicity: The Context API is built into React and is more straightforward to set up, making it a more convenient choice for simpler state needs.

2. Single Point of Configuration: Context API allows for a centralized point of configuration for state, similar to Redux.

3. Easier to Understand for Smaller Apps: It's less intensive and thus, is easier to explain and understand, especially for junior developers or in smaller teams.

When to Pick Context API

• When No Nested Components: Great for smaller applications or ones with minimal nesting of components, eliminating the need to prop-drill or create additional HOCs or render-props to share state.

• For App-Wide Configurations: It's useful for handling global configurations, such as themes or user authentication.

• Newer React Projects Involving Hooks: Since the Context API underwent significant improvements with the introduction of Hooks, it's an appealing choice for new projects.