Capgemini Engineering Interview Questions and Answers

Let, Const, and Var are used to declare variables in JavaScript with different scoping and reassignment abilities.

• Var has function scope and can be redeclared and reassigned.

• Let has block scope and can be reassigned but not redeclared.

• Const has block scope and cannot be reassigned or redeclared.

State and props are two important concepts in React. State represents the internal data of a component, while props are used to pass data from a parent component to a child component.

• State is mutable and can be changed within a component.

• Props are read-only and cannot be modified within a component.

• State is used to manage component-specific data, while props are used for inter-component communication.

• State is initializ...read more

Promise is a callback function that returns a value in the future. Async-Await is a syntax that simplifies working with Promises.

• Promises are used to handle asynchronous operations and avoid callback hell.

• Async-Await is a syntax that allows writing asynchronous code that looks like synchronous code.

• Async-Await is built on top of Promises and uses the same underlying mechanism.

• Async-Await can only be used within an asyn...read more

Closures are functions that have access to variables in their outer scope, even after the outer function has returned.

• Closures are created when a function is defined inside another function.

• The inner function has access to the outer function's variables and parameters.

• Closures can be used to create private variables and methods.

• Closures can also be used to create functions with pre-set arguments.

Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their scope.

• Hoisting applies to both variable and function declarations.

• Variable declarations are hoisted but not their initializations.

• Function declarations are fully hoisted, including their definitions.

• Hoisting can lead to unexpected behavior if not understood properly.

Event Loop is a mechanism that allows JavaScript to handle asynchronous operations.

• Event Loop is a continuous process that checks the Event Queue and moves events to the Event Stack.

• Event Queue holds all the events that are waiting to be processed.

• Event Stack holds the events that are currently being processed.

• When the Event Stack is empty, the Event Loop checks the Event Queue for new events.

• JavaScript uses Event Loop...read more

ES6 introduces new syntax and features to JavaScript, enhancing code readability and functionality.

• Arrow Functions: Shorter syntax for function expressions. Example: const add = (a, b) => a + b;

• Template Literals: Multi-line strings and string interpolation. Example: const greeting = `Hello, ${name}!`;

• Destructuring Assignment: Unpacking values from arrays or properties from objects. Example: const [a, b] = [1, 2];

• Def...read more

Local Storage is persistent storage that remains even after the browser is closed, while Session Storage is temporary and is cleared when the browser is closed.

• Local Storage has no expiration date, while Session Storage is cleared when the session ends

• Local Storage can store larger amounts of data compared to Session Storage

• Local Storage is accessible across different browser tabs and windows, while Session Storage is ...read more

Redux is a state management library for JavaScript applications, providing a predictable and centralized workflow.

• Redux follows a unidirectional data flow pattern.

• The application state is stored in a single JavaScript object called the store.

• Actions are dispatched to describe state changes.

• Reducers are pure functions that specify how the state should change based on the dispatched actions.

• Selectors are used to extract ...read more

Optimizing a React app involves reducing bundle size, using lazy loading, and optimizing rendering performance.

• Reduce bundle size by code splitting and using dynamic imports

• Use lazy loading to load components only when needed

• Optimize rendering performance by using shouldComponentUpdate and PureComponent

• Use React.memo to memoize functional components

• Avoid unnecessary re-renders by using useMemo and useCallback

• Use perfor...read more

Hooks are a feature introduced in React 16.8 that allow developers to use state and other React features in functional components.

• useState() - for managing state in functional components

• useEffect() - for performing side effects in functional components

• useContext() - for accessing context in functional components

• useReducer() - for managing complex state and actions in functional components

• useCallback() - for memoizing f...read more

Higher Order Functions are functions that take other functions as arguments or return functions as their results.

• Higher Order Functions can be used to create reusable code by abstracting common functionality into a separate function.

• They can also be used to implement functional programming concepts like currying and composition.

• Example: Array.prototype.map() is a higher order function that takes a callback function as ...read more

Context API is a feature in React that allows data to be passed down the component tree without manually passing props at each level.

• Context API provides a way to share data between components without the need for prop drilling.

• It consists of two main components: Provider and Consumer.

• The Provider component allows data to be provided and accessed by any component within its subtree.

• The Consumer component allows compone...read more

React class components have a lifecycle that includes mounting, updating, and unmounting phases with specific methods for each.

• Mounting: Methods called when a component is being created and inserted into the DOM. Key methods: constructor(), render(), componentDidMount().

• Updating: Methods called when a component's state or props change. Key methods: shouldComponentUpdate(), render(), componentDidUpdate().

• Unmounting: Met...read more