December 15, 2022

React Interview Questions Interview Prep with Answers and Examples

It is scoped to a single component and cannot leak to any other element in the page. Refs can be created by using React.createRef() and attached to React elements via the ref attribute. It is commonly assigned to an instance property when a component is created, and then can be referenced throughout the component. In React, Higher Order Component is an advanced technique for reusing component logic. It is a function that takes a component and returns a new component.

  • Context passes the data from a parent to every child of it, which is marked as a context consumer.
  • In React, a functional component is a plain JavaScript function that takes in props and returns a React element.
  • React has a huge ecosystem of libraries and provides you the freedom to choose the tools, libraries, and architecture for developing the best application based on your requirement.
  • They can dynamically accept one or more components as children without modifying or copying any of the children’s behavior.
  • It gives us expressiveness of JavaScript along with HTML like template syntax.
  • It should be noted that context should be used sparingly, as it can make your components more difficult to reason about and test.

In this example, the useIntl hook is used to access the intl object, which provides internationalization functions like formatDate. The FormattedMessage component is used to display a localized message with the ID greeting. A synchronous action is an action that is dispatched and immediately processed by the Redux store. The store updates the state, and the updated state is immediately available for consumption by the components. Server-side rendering (SSR) is when the initial render of a React application is done on the server. The server generates the HTML for the initial state of the application and sends it to the browser.

Define Your Event Handler as an Arrow Function Assigned to a Class Field

As stated by the react team, virtual DOM is a concept where a virtual representation of the real DOM is kept inside the memory and is synced with the real DOM by a library such as ReactDOM. For updating the state, we need to first bind the addStudent function to this. Only then, we will be able to use the setState function which is used to update the state. React JS Coding Interview Challenges and Exercises… However, the React docs prefer this method of using the previous state value – passing a function that receives the previous state value.

React.js was released for use in 2015 and since then it has become one of the most trusted and used technologies of recent time. It has built one of the largest developer communities around itself. React is an open-source JavaScript frontend library for creating user interfaces. It uses component based approach to create complicated, interactive web and mobile user interfaces.

How does the Real DOM differ from the Virtual DOM?

One key difference between the two is that a class component can have local state and lifecycle methods, while a functional component cannot. However, starting with React 16.8, functional components can also have a state using hooks. There are several ways that an error can be handled in a React application. Using a try-catch block in a component’s lifecycle routines, like componentDidCatch, is a common way to manage rendering-related issues. An alternate approach is to construct a component that detects problems that occur inside its child components using the Error Boundaries feature. Additionally, you may control errors that occur inside a functional component by combining a try-catch block with the useEffect hook.

You don’t actually have to use JSX to create React components and can use React.createElement() instead, but Facebook recommends using JSX. Most React developers prefer its declarative syntax, and it also reduces code complexity. With this question, the interviewer wants to find out if you know about the JavaScript ecosystem in general and what makes React unique. One thing you could bring up is that while some developers call React a framework, many consider it a library and not a full framework.

What types of hooks are there in React? How to handle the lifecycle inside the hooks properly?

Earlier, refs were only limited to class components but now it can also be accessible in function components through the useRef Hook in React. Whenever the value of the input element is changed, event-based callbacks are not called. Basically, react does not perform any action when there are changes made to the input element. Controlled and uncontrolled components are just different approaches to handling input from elements in react.

It’s used to perform asynchronous operations and dispatch multiple actions. Thunks allow you to write action creators that return a function instead of an action. The inner function receives the store’s dispatch method as an argument, which can be used to dispatch actions at any point in the future. Thunks are typically implemented using a middleware, such as the redux-thunk middleware.

React Basics — React Interview Questions

Autobinding automatically binds our functions to the React Component instance so that passing the function by reference in the render() works seamlessly. Invoking thing.speak() in the console will log “jen”, but pressing a key will log undefined because the context of the callback is the global object. The browser’s global object – window – becomes this inside the speak() function, so becomes, which is undefined. Can be applied at any level of an application component hierarchy, which allows it to be adopted incrementally within a codebase.

front end developer react js interview questions

The key difference between the two is the way they manage and manipulate data. An asynchronous action, on the other hand, is an action that is dispatched but takes some time to complete. Asynchronous actions are typically used when performing network requests or doing other operations that take time.

React renders each of these components independently without affecting the rest of the application UI. Hence, we can say that, in React, everything is a component. React provides a lot of handy tools that can make the task of the developers understandable and easier. Use these tools in Chrome and Firefox dev extension, allowing us to inspect the React component hierarchies in the virtual DOM. It also allows us to select the particular components and examine and edit their current props and state. React comes with good availability of documentation, tutorials, and training resources.

front end developer react js interview questions

The basic usage of a custom hook is to extract a function’s logic into its own component. UseState() method is your go-to resource for state management in a functional component. The apply method is used to call the callback function with the object that it was initially called with, applying the arguments and context to it. The most commonly asked questions (generally at the start of the interviews) are about array methods. The interviewer wants to asses how comfortable you are with array manipulation. But remember, even if the company you’re interviewing with relies heavily on React, they’ll likely test your knowledge of other programming tools and functions.