Javascript Technical Interview Questions

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Michael Zippo 04.11.2021

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React’s popularity has grown significantly in popularity in recent years.

According to the 2019 Stack Overflow Developer Survey, which studied development tools and practices used by over 90,000 programmers, React. js was the second most popular web framework among respondents.

React has become so popular because it gives developers the ability to quickly build scalable applications, a value that many companies around the world have recognized. As a result, React interview questions are common in web development job interviews.

In this guide, we explore the 15 most common React.js interview questions in job interviews and give you tips on how to answer them like an expert. We’ll focus on theoretical questions designed to test your knowledge of the React ecosystem.

# 1: what is React JS

In an interview this might seem like a simple question to ask; you may even think it’s a gimmick. However, it is a very common question in interviewing people. ’hiring techniques precisely because it’s so simple.

Here are a few points you should cover in your answer:

• React is a library Front-end JavaScript for building web apps.
• React is declarative, which means you can design simple views for each state of a We app. b.
• React uses components, which allow you to create reusable elements on a web page.

# 2: What is the difference between accessories and condition ?

Accessories and condition are two essential concepts you should be familiar with in order to pass data through components .

State refers to the default data value in a React component. The state of a component can change over time and can be changed manually by a developer. Accessories, on the other hand, describe how a React component is configured. The accessories do not change.

# 3: what are React components?

Components are a core feature of React - they are the building blocks of all React-based applications. You need to know this and be able to describe what a component is.

Components allow developers to break up a user interface into smaller parts that can be reused. React renders each component on a web page only when needed, allowing applications to display faster.

# 4: When are keys used in React ? < / h2>

Keys are used in React to identify unique elements in the virtual DOM Using keys React can optimize rendering because the framework can recycle existing elements loaded into the DOM.

Suppose we have two instances of a component on a th web page. Without keys, React would render both elements in the DOM and not rearrange the El DOM elements. But, when using keys, React rearranges the DOM elements, which provides a number of performance benefits to an application.

# 5: What are the most common approaches to styling a React component?

There are several ways to model a React component, and you should be able to describe how they work. Here are the main ways React components are styled:

• CSS classes. React - allows you to use traditional CSS class names to define styles for a component
• Inline CSS: Inline CSS allows you to define styles in a particular element of a web page.
• JavaScript Modules: JavaScript modules such as styled-jsx and stylized components are also used to style components.
• Preprocessors: Preprocessors like Sass and Less are another option for styling a component.

# 6: When you need to use a class component instead of a functional component

There are two component types in React: class and functional.

Functional components are defined by a component with immutable properties (accessories). Class components, on the other hand, are more complex components that allow you to manage the state of a component.

You must use class components on a functional component when you need to manage the state of a component. component or use component lifecycle methods.

# 7: What Happens During the Lifecycle of a React Component ?

The lifecycle of a React component are the events that occur from the creation of a component until its destruction.

Three main parts make up the lifecycle of a React component: initialization, state update, and destruction.

For example, when creating a component, you can use methods such as componentDidMount () to add event listeners to the component. This happens after the initialization of a component. Then you can use componentWillUnmount () to outrun an event listener when the component is about to be removed from the web page.

# 8: What is a virtual DOM ? How does it work ?

When an HTML document is rendered by a web browser, a representative tree called the Document Object Model (DOM). This provides the browser with all the information it needs to properly display a web page.

By default, a web page will use HTML to update its DOM and make changes to the page (like updated content that appears on a website). React, on the other hand, creates a virtual DOM, which is a copy of the "real" web page. DOM.