Basic JavaScript Interview Questions

What are the major features of React?

React is a popular JavaScript library for building user interfaces, primarily for single-page applications. Major features include Virtual DOM, JSX syntax, Component-Based Architecture, One-way data binding with props, and the ability to manage application state with hooks, making it a go-to for cronj interview questions for reactjs.

What is JSX?

JSX (JavaScript XML) is a syntax extension for JavaScript. It isn't necessary to use React, but it is recommended for describing what the UI should look like. JSX might remind you of HTML, making it one of the key react js interview questions for freshers.

What is the difference between Element and Component in React?

An element is a plain object describing what you want to appear on the screen in terms of the DOM nodes or other components. Components, on the other hand, are reusable pieces of code that return a React element to be rendered to the page. This distinction is a common area for react js interview questions.

How to create components in React?

Components in React can be created either as a class component or a function component. Class components involve creating a class extending from React.Component and implementing a render method. Function components, on the other hand, are simple JavaScript functions. They are a critical area of React and often form part of cronj react interview questions.

When to use a Class Component over a Function Component?

You should consider using Class Components when you require lifecycle methods or if you need to manage state within the component. However, with the advent of React Hooks, function components can also manage state and handle lifecycle events. This comparison is a regular on react node interview questions.

What are Pure Components?

Pure Components in React are a simpler way to write functional components when they can be expressed as a pure function of their props. These components perform a shallow comparison on new and old props/state and render only when they detect changes. This concept makes up for significant react js interview questions for 5 years experience.

What is state in React?

State is a built-in object in React that stores component data that can change over time. The state is initialized in the constructor and then updated with the setState() function, adding depth to the cronj interview questions for reactjs.

What are props in React?

Props (short for properties) are read-only objects which are used to pass data from parent to child components, a fundamental concept to understanding react js interview questions for freshers.

What is the difference between state and props?

State is a data structure that starts with a default value and may change over time, while props are read-only components that the parent passes into the child. Grasping this difference can help you navigate react interview questions for 5 years experience.

Why should we not update the state directly?

Directly modifying the state is a common pitfall in React. It leads to potential errors and inconsistencies in the UI because React may batch multiple setState() calls into a single update for performance. Therefore, it is advisable to use the setState() function for updating the state. This is a pivotal caution emphasized in many react js interview questions.

What is the purpose of callback function as an argument of setState()?

The callback function in setState() is used for any post action once the state has been updated. This ensures that the update has been applied, making it a common topic in react js interview questions for 5 years experience.

What is the difference between HTML and React event handling?

In HTML, event names are in lowercase, whereas in React they use camelCase. Also, in HTML, you can return false to prevent default behavior, but in React, you must call preventDefault() explicitly, distinguishing points for react and node js interview questions.

How to bind methods or event handlers in JSX callbacks?

Methods in React component classes are not bound by default. They can be bound using .bind(this) in the constructor, arrow functions, or using class fields syntax, an essential react interview questions.

How to pass a parameter to an event handler or callback?

Parameters can be passed to event handlers or callbacks using an arrow function, a point often explored in cronj react interview questions.

What are synthetic events in React?

React implements a SyntheticEvent system, which is a cross-browser wrapper around the browser's native event system, appearing frequently in react js interview questions.

What are inline conditional expressions?

In JSX, you can include any JavaScript expression within curly braces and use it with conditional (ternary) operators, making inline conditional expressions an interesting topic for react interview questions for freshers.

What is "key" prop and what is the benefit of using it in arrays of elements?

The key prop helps React identify which items have changed, added, or removed, thereby aiding efficient re-rendering of components, a crucial part of react js interview questions.

What is the use of refs?

Refs are used to access DOM nodes or React elements directly within components, a fundamental topic for react node interview questions.

How to create refs?

Refs are created using React.createRef() and attached to React elements via the ref attribute, a common area in react js interview questions for freshers.

What are forward refs?

Forwarding refs allow passing a ref through a component to one of its children. This is a useful feature in some situations and often discussed in react js interview questions for 5 years experience.

Which is preferred option with in callback refs and findDOMNode()?

The preferred way is to use callback refs over findDOMNode() as the latter can be more brittle and may cause issues in future React versions, a frequent question in cronj interview questions for reactjs.

Why are String Refs legacy?

String refs have some issues, they are considered legacy and should be avoided. They can cause name clashes and don't play well with static analysis tools, often discussed in cronj react interview questions.

What is Virtual DOM?

The Virtual DOM is a programming concept where an ideal, or "virtual", representation of the UI is kept in memory and synced with the "real" DOM via a process called reconciliation, making it a fundamental area in react js interview questions.

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