Home 9 Daniel Zacharias 9 Top React Interview Questions and Answers for Beginners

Top React Interview Questions and Answers for Beginners

To prepare like a real pro web developer for your job interview, an unshakable foundation of React is a must-have. It'll also give you an advantage when creating your first React tools. These most common questions will help you achieve that, so let's start with the basics.
Daniel Zacharias

Daniel Zacharias

September 5, 2023
React

Riddle me this: What’s a library, not a framework, is declarative and component-based, and powers up the UIs of Facebook and Instagram?

If you answered React, congrats! You surely know your development tools. Of course, that’s only the beginning when it comes to a library as powerful and widely used as React. If you’re just getting started with it, there’s plenty more to learn. That’s especially true if you aspire to work with it. 

When applying to your first React job, there will be a lot more than simple riddles and questions. During the interview, HR is infamous for stress-testing your React knowledge. At least, that was the case when I started my React journey. 

But don’t worry, with questions I’m about to uncover, you’ll walk into that interview room with the confidence of a seasoned React professional! 

Master the basics: 3 essential react interview questions answered

Let’s start with the basics. 

To prepare like a real pro web developer for your job interview, an unshakable foundation of React is a must-have. It’ll also give you an advantage when creating your first React tools.

These most common questions will help you achieve that:

Q1: How would you describe React and its purpose?

In 2013, Facebook introduced React: a front-end JavaScript library that focuses on crafting interfaces for single-page applications. From that point on, it changed the web development industry forever!

Its main objective is to let developers produce reusable UI components, leading to consistent, swift, and effective development processes.

Q2: How would you describe the difference between a class component and a functional component in React?

Class components — They are considered ES6 classes that extend from React.Component. Think of them as the VIPs of React. They feature:

  • lifecycle methods
  • states
  • props
  • larger project support

Functional components — simple JavaScript functions accepting props as an argument. They were very limited before React Hooks came along since they used to be stateless and couldn’t pack any lifecycle methods or states. 

With the introduction of Hooks, their functionality skyrocketed!

Both of them are equally important. Whether you’re building a small project requiring few reusable UI components or working on something more complex benefiting from sophisticated state management, they will be your right hand in React development.

Q3: How would you describe JSX in React?

JSX (JavaScript XML) is primarily used with React to define the app’s UI structure. It might look like HTML at first sight, but wait till you see what it can do! 

This powerful tool allows you to write HTML in React effortlessly without stressing how it would affect the core functionalities of your application. With the power of JSX on your side, writing engaging user interfaces has never been easier.

Component magic: 4 interview questions about React’s core

Fact: React components are the building blocks of modern-day applications. 

Understanding them to the core with these answers will give you an upper hand during an interview:

Q1: What are the key features of a React component?

React has two component pillars — State and props. 

The state represents the part of the data that can change over time. It’s internal to a component and influences the component’s behavior, rendering, and functionality. The state is always easily updated in response to event handlers, server responses, or prop changes using the setState() method.

Props (short for properties) — these little guys are read-only components. Their only purpose is to give instructions on how components should be configured. They’re passed from one parent component to a child component and can’t be changed within the child. 

Props play an essential role in preventing unwanted errors or inconsistencies in your code since they produce clear boundaries between each component.

You’ll find them both in both functional and class components. In functional components, props are passed as an argument to the function, while in class components, props are accessed using the this.props object.

Q2: How would you explain the lifecycle of a React component?

If I had a penny every time HR with a little bit of web dev knowledge asked this question, I’d be a millionaire!

But hopefully, you’ll become one knowing that every React component has three main phases in its lifecycle. They are:

  • Mounting — It’s all about creating and inserting your app’s components into the DOM. You might think of this phase as the moment when the curtain rises on your app’s big premiere.
  • Updating —  The moment when things start to get exciting! This phase is triggered when there are changes in either props or state, which means the components need an update. It’s like optimizing your favorite game for better performance. Everything just runs smoother.
  • Unmounting — It’s like closing the curtains after a memorable performance. In this final stage, your component gets removed from the DOM because its services are no longer needed.

Q3: What are Higher-Order Components (HOCs) in React?

This one is tough. It’s where most junior React developers fall short.

Think of Higher-Order Components (HOCs) as all-mighty functions designed to add extra properties or behaviors to components. They’re like the superheroes of your app, giving you the superpower of reusing component logic.

With HOCs, the component composition isn’t only achievable but effortless! Using them, putting together different parts of a component is like putting together your favorite LEGO set (beautiful and incredible in the end).

Q4: How would you describe the significance of keys in React?

Keys in React are like individualized IDs that you give to different elements in a list or array. They help your app identify which items have been added, changed, or removed and determine whether it should display these changes or let them be.

Using keys is a secret trick to boosting React’s performance as they reduce the need to re-render entire components. In other words, it’s like putting a laser in your hands for pointing out what exactly has changed, making for faster and smoother user experiences!

Bonus question!

Q: Can you explain what stateful and stateless components are in React?

The trickiest question of them all in the React component section!

The main difference is stateful components (some even call them container components, but that’s an injustice in my opinion) maintain and update their state over time, hold the business logic together, and serve as a container for other stateless components.

Stateless components are equally valuable, but they only render information that originates from their props. They can’t maintain any state themselves but operate entirely on external input.

State and props mastery: How to ace these React interview questions

Let’s expand further on the topic of state and props in React development. HR likes to focus on it, so let’s prepare you to the fullest!

Q1: How do you handle the state in React?

There are different ways to answer this one, but every alternative falls back to the core – The state in React is managed within the component. It can also change over time, thanks to fantastic features like useState Hook (for functional components) or this.setState method (for class components). 

These updates happen asynchronously and depend on previous states.

The rule of thumb is: The more accurately you manage your app’s state, the better its robustness becomes.

Q2: How would you pass a state from a parent component to a child component?

In React, the state is passed from parent to child component through these three prop stages:

  1. Define the state in the parent component.
  2. Pass it as a prop to the child component.
  3. Access it within the child component using the props object.

After the newly acquired state is accessed through the handy props object every section of your component is the perfect alignment.

Q3: How would you handle a situation where a child component needs to pass data to a parent?

While data usually flows down the component hierarchy from parent to child, it’s sometimes necessary for a child component to communicate with its parent. In these circumstances, functions are the go-to solution.

It all starts with the parent – they define a function that they pass on as props to their child component. This newly inherited function can then be invoked by the child whenever there’s a change or event. 

This way, through swift communication techniques, both components are always kept up-to-date regardless of their hierarchical level.

Q4: What is the difference between default props and the initial state in React?

Don’t get it twisted — default props and initial state are one of the most confusing things in the state-prop aisle. But they serve completely different purposes in the grand React ecosystem.

Default props in React are a safety net for components. They define default values for props. 

They come into action when a particular prop isn’t provided when instantiating a component. 

Here’s what they look like:

class WelcomeMessage extends React.Component {

  static defaultProps = {

    name: ‘Anonymous’

  };

  render() {

    return <h1>Hello, {this.props.name}</h1>;

  }

}

The initial state is the state value when the component mounts for the first time. It’s a concept that revolves around how a component manages, handles, and tracks change within itself. 

The initial state of a component is defined in the constructor of a class component or the useState hook of a functional component. 

Here’s how the initial state looks in practice:

class Counter extends React.Component {

  constructor(props) {

    super(props);

    this.state = {

      count: 0

    };

  }

  // … 

}

Q5: How would you pass a function as a prop in React?

I’ll give you a secret: Passing functions as props is one of the best practices you’ll learn as a React developer. It’s a powerful technique allowing for efficient data transfers between components and supports bi-directional communication from parents to children.

The parent component passes a function to the child via props — a well-known runtime object that stores all sorts of component information. The child can then trigger this newly acquired function whenever there are changes or events, thus enabling better interactivity within your app.

Here’s what it looks like in the code:

class ParentComponent extends React.Component {

  handleChildClick = () => {

    console.log(‘Button clicked in Child Component’);

  };

  render() {

    return <ChildComponent onClick={this.handleChildClick} />;

  }

}

class ChildComponent extends React.Component {

  render() {

    return <button onClick={this.props.onClick}>Click Me</button>;

  }

}

Routers and Redux: Turning complex React interview questions into simple answers

React Router and Redux are the backbone libraries without which React’s ecosystem would crumble. They are also the most mentioned libraries during interviews, so you better get prepared with these questions:

Q1: What is React Router, and why is it important?

React Router gives you unparalleled capabilities when it comes to navigation between screens and flows. By maintaining the standard structure and behavior of your applications, you can create single-page, multi-view web apps that are optimized for user engagement.

What makes React Router so crucial is its ability to keep UIs in sync with URLs. It lets you easily navigate through different views on a website while enjoying fluid transition animations along the way! 

Additionally, Router remembers your state when moving forward or backward through pages, making for an even more efficient and engaging app experience.

Q2: What are the key components of React Router?

React Router consists of three core components:

  1. <BrowserRouter>: This is a type of <Router> that uses the HTML5 history API to keep your UI in sync with the URL in a web application.
  2. <Route>: This component is conditionally shown based on matching the current URL. It allows you to render a UI when the path matches the current URL.
  3. <Link>: This is a component that provides declarative, accessible navigation around your application. It’s analogous to using a <a> tag in HTML but provides additional features useful in a single-page app environment.

Q3: What is Redux and why would you use it?

React’s Redux offers incredible features for managing the app’s state. It’s also most commonly used with other libraries, such as Angular for building modern UIs.

Redux’s main power comes from eliminating the guesswork when transitioning states. By ensuring that your state transitions are explicit and easily predictable, you can avoid costly errors that could ruin an otherwise seamless user experience. 

Q4: Can you explain the concept of ‘actions’ in Redux?

In Redux, actions serve as the exclusive source of information for your store. They’re attached to payloads of data that transfer needed information from your application over to your store. 

These plain JavaScript objects must contain a type property indicating what type of action you’re performing, and can also carry a payload property with updated data.

Once an action is created, it’s time to trigger a state change – and that’s where dispatching comes in! 

It’s done by calling the store. dispatch() signals to Redux that it’s time for an update, setting off a chain reaction throughout your app, and ensuring everything is accurate and on point.

Acing your React interview – TL;DR

Riddle me this last one: What combines JavaScript fundamentals, components, state, props, routers, and Redux into a fearsome tech challenge?

 It’s your first React interview! With these insights under your belt, you’re all set to ace it. So go forth, and conquer the React realm!

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