Junior Web Developer Interview Questions and Answers for Freshers

Real DOM is the actual DOM in the browser, while Virtual DOM is a lightweight copy used for performance optimization.

• Real DOM updates are slow and inefficient due to direct manipulation of the actual DOM elements.

• Virtual DOM is a virtual representation of the actual DOM, allowing for faster updates and improved performance.

• React uses Virtual DOM to update only the necessary parts of the actual DOM, reducing unnecessary re-renders.

Closure is a function that has access to its own scope, even after the function has closed.

• Closure allows a function to access and manipulate variables from its outer scope.

• Use closure when you want to create private variables or functions that are only accessible within a specific scope.

• Example: Creating a counter function using closure to maintain the count state.

Promises in JavaScript are objects representing the eventual completion or failure of an asynchronous operation.

• Promises help to handle asynchronous operations in a more organized and readable way.

• They can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained together using .then() to handle success and .catch() to handle errors.

• Example: const myPromise = new Promise((resolve, reject) => { ... });

Session in PHP is a way to store information (variables) to be used across multiple pages during a user's visit to a website.

• Sessions are used to store user-specific information, such as username, shopping cart items, etc.

• Sessions are started with session_start() function and can be accessed using the $_SESSION superglobal array.

• Sessions are stored on the server and identified by a unique session ID, which is usually stored in a cookie on the user's browser.

HOC (Higher Order Component) in Reactjs is a pattern where a function takes a component and returns a new component.

• HOC allows code reuse, logic abstraction, and props manipulation in React components.

• Example: withAuth HOC can be used to restrict access to certain components based on user authentication.

• HOC can be created using a function that takes a component as an argument and returns a new component with additional props or functionality.