FrontEnd Developer Interview in Cognizant2 4 yrs by Sona Frontend Weekly

In this example, the Router component is used to wrap the entire application and the Route component is used to define the specific routes and the components they map to. The exact prop is used to ensure that only the exact path is matched and not any subpaths. Predictability of outcome –Since there is always one source of truth, i.e. the store, there is no confusion about how to sync the current state with actions and other parts of the application. Synthetic events are the objects which act as a cross-browser wrapper around the browser’s native event. This is done to make sure that the events show consistent properties across different browsers. Once the component gets added to the DOM, it can potentially update and re-render only when a prop or state change occurs.

React Native uses native components, which means that the applications built with it have a look and feel that is similar to that of native mobile applications. A component is a self-contained, reusable piece of code that can be composed using other components to create complex user interfaces. In React, a component can represent anything from a simple button to a complex form or a complete application. Redux follows a unidirectional data flow pattern, which means that the data flows in only one direction in the application. Redux stores the entire application state in a single store, which is managed by reducers. Reducers are functions that take the current state and an action to return a new state.

React.js interview questions and answers for experienced engineers

Use test-driven development to write tests before writing the implementation code for a feature. Write unit tests for individual React components to ensure that they are working correctly in isolation. For example, you might have an action called ADD_TODO that adds a new to-do item to the array, and a reducer that updates the state accordingly. You could also have an action called SET_LOADING that updates the loading state. Of course, experience comes with time but some of you may have the mindset of a senior developer but not studying the required topics. Without React, your website or app will use HTML to update its DOM in order to make things “change” on screen without users needing to manually refresh a page.

By simply updating the store, developers are able to manage and test any react component. All the applications are highly scalable and suffer no compatibility issues. With these well-crafted front-end developer interview questions, you are now very aptly equipped to design and answer any questions regarding front-end development. However, these front-end developer interview questions only cover the technical aspect of the interview. An interview doesn’t just gauge the technical prowess of a candidate. Apart from preparing these front-end developer interview questions, you would also need to work on your soft skills and social life as a front-end developer.

Example Basic React Interview Questions and Answers

A stateless component, also known as a “dumb” or “presentational” component, is a component that does not maintain its own internal state. It receives data and callbacks through props and only renders the UI based on those props. Stateless components are typically used for simple, presentational elements that don’t need to handle any complex logic or internal state updates. Presentational components are usually responsible for rendering UI elements to the screen, and they tend to be functional components that receive data and callbacks as props.

Use this as an opportunity to return false when you’re certain that the transition to the new props and state will not require a component update. Shallow rendering is less similar to real-world usage of a component as part of an application, so it may not catch certain problems. Within a real application, if the component is broken and throws an error, then would fail to render. However, if the unit tests of only use shallow rendering, then this issue will not be identified unless is also covered with unit tests. It is faster to shallow render a component than to fully render it.

Top 75+ Frontend Developer Interview Questions and Answers

Their answer will show you the depth of their understanding of React and its concepts. The component will render the specified component when the current URL matches the route’s path. You can use the exact prop to specify that the route should only be matched when the path is exactly the same as the current URL.

• The container is the DOM element that the child component should be rendered into, and the child component is any renderable React child, such as an element, string, or fragment.
• In this guide, you‘ll find example ReactJS interview questions and answers you can refer to when seeking a new ReactJS developer to make your dynamic user interfaces come to life.
• If you want to read more about the use of Angular, browse through our Angular interview questions and answers to get a deeper understanding of the framework.
• Hydrating the components on the client so that they can be interactively controlled by the user.
• This can involve a combination of unit tests, integration tests, and end-to-end tests, as well as techniques such as snapshot testing and TDD (test-driven development).
• However, it takes more time to update the DOM and results in a number of unnecessary updates by many JavaScript frameworks.
• Firstly the react runs the diffing algorithm to identify the changes that are made in the virtual DOM.

Otherwise, initialValue which was provided is set as the default value. Debouncing is a method of preventing a function from being invoked too often, and instead waiting a certain amount of time until it was last called before invoking it. Simply put, a polyfill is a custom implementation of native JavaScript functions. The interviewer wants to asses how comfortable you are with array manipulation. Event handlers are a key part of React’s event handling system and are used to add interactivity to your application.

Nodejs Developer Roadmap 2023

CloneElement is utilized as a part of a request to clone a component and pass it new props. You can’t ensure the AJAX request won’t resolve before the component mounts. In the event that it did, that would imply https://wizardsdev.com/en/vacancy/front-end-developer-react/ that you’d be attempting to setState on an unmounted component, which won’t work, as well as React will holler at you for. Doing AJAX in componentDidMount will ensure that there’s a component to update.

The Profiler tool allows developers to find components that take a long time to render or are rendering more frequently than necessary. React components can be reused across your application, making it easier to maintain and update your code. For example, you can create a button component and reuse it throughout your application instead of writing the same code multiple times. We all know that choosing the right candidate for your company is a challenging task. This occupation requires a good set of basic React js interview questions to assess the employee’s knowledge and skills.

What are React events?

Keys are used for identifying unique Virtual DOM Elements with their corresponding data driving the UI. They help React to optimize the rendering by recycling all the existing elements in the DOM. These keys must be a unique number or string, using which React just reorders the elements instead of re-rendering them.

Before starting his career as a writer and content marketer, he spent 10 years as a full-time parent to his daughters Veronica and Athena. React uses this copy to determine what parts of the actual DOM need to change based on a user’s action. React then takes the change date from the Virtual DOM and selectively updates the actual DOM . Over time, this leads to significant performance improvements for the website or application.