Cognizant Senior Software Engineer Interview Questions and Answers

Custom hooks in React are reusable functions that allow you to extract component logic into separate functions for better code organization and reusability.

• Custom hooks are created using the 'use' prefix and can be used to share logic between components.

• Use cases for custom hooks include fetching data from an API, handling form state, managing local storage, and more.

• Example of a custom hook for API call: const useFetc...read more

useMemo is used to memoize a value, while useCallback is used to memoize a function.

• useMemo is used to memoize a value and recompute it only when its dependencies change.

• useCallback is used to memoize a callback function and prevent unnecessary re-renders.

• Example: useMemo can be used to memoize the result of a complex computation, while useCallback can be used to memoize an event handler function.

Class-based components use ES6 classes and have lifecycle methods, while functional components are simpler and use functions.

• Class-based components use ES6 classes to create components, while functional components are created using functions.

• Class-based components have lifecycle methods like componentDidMount and componentDidUpdate, while functional components do not.

• Functional components are simpler and more lightweig...read more

Implementing the lifecycle of a React component in a functional component

• Use the useEffect hook to replicate lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount

• Pass an empty array as the second argument to useEffect to mimic componentDidMount

• Pass a variable or state as the second argument to useEffect to mimic componentDidUpdate

• Return a cleanup function inside useEffect to mimic compo...read more

Various state management techniques in React include Context API, Redux, and local state.

• Context API: React's built-in solution for passing data through the component tree without having to pass props down manually at every level.

• Redux: A popular state management library for React applications, allowing for a centralized store to manage application state.

• Local state: Managing state within individual components using us...read more

Redux is a predictable state container for JavaScript apps. Middlewares are functions that intercept actions before they reach the reducer.

• Redux follows a unidirectional data flow architecture.

• Middlewares in Redux are functions that can intercept, modify, or dispatch actions.

• Common use cases for middlewares include logging, asynchronous API calls, and handling side effects.

• Examples of popular Redux middlewares are Redu...read more

Hoisting in JavaScript is the behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase.

• Variable declarations are hoisted to the top of their scope, but not their initializations.

• Function declarations are fully hoisted, meaning they can be called before they are declared.

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

Event bubbling is the propagation of events from the target element up through its ancestors in the DOM tree.

• Events triggered on a child element will 'bubble up' and trigger on parent elements.

• Event listeners can be attached to parent elements to handle events from multiple child elements.

• Stopping event propagation can be done using event.stopPropagation() or event.stopImmediatePropagation().

Block scope and function scope are two types of scopes in JavaScript that determine the visibility and accessibility of variables.

• Block scope refers to the visibility of variables within a block of code enclosed by curly braces. Variables declared with 'let' and 'const' have block scope.

• Function scope refers to the visibility of variables within a function. Variables declared with 'var' have function scope.

• Variables de...read more

Yes, I have experience working with semantic tags in HTML.

• Used semantic tags like <header>, <nav>, <main>, <section>, <article>, <aside>, <footer> for better structure and SEO.

• Understand the importance of using semantic tags for accessibility and search engine optimization.

• Semantic tags help in organizing content and making it more readable for developers and browsers.

Various methods for creating an object in JavaScript include object literals, constructor functions, ES6 classes, and Object.create() method.

• Object literals: var obj = { key: value };

• Constructor functions: function ObjectName() { this.key = value; } var obj = new ObjectName();

• ES6 classes: class ClassName { constructor() { this.key = value; } } var obj = new ClassName();

• Object.create() method: var obj = Object.create(pr...read more

Shallow copy only copies the references of nested objects, while deep copy creates new copies of nested objects.

• Shallow copy creates a new object but does not create copies of nested objects, only copies their references.

• Deep copy creates a new object and also creates new copies of all nested objects.

• Shallow copy can be achieved using Object.assign() or spread operator, while deep copy can be achieved using JSON.parse(...read more

The code will throw an error because 'a' is declared but not initialized.

• The code will result in a ReferenceError because 'a' is declared but not assigned a value.

• Variables declared with 'const' must be initialized at the time of declaration.

• Initializing 'a' with a value before calling test() will prevent the error.

CSS can be used to arrange elements in a row and column layout using flexbox or grid layout properties.

• Use display: flex; for a row layout and display: flex; flex-direction: column; for a column layout

• Use justify-content and align-items properties to align items in the main axis and cross axis respectively

• For grid layout, use display: grid; and grid-template-columns or grid-template-rows to define the layout

Yes, I have utilized CSS preprocessors such as SASS and LESS.

• I have experience using SASS to streamline my CSS workflow by utilizing variables, mixins, and nesting.

• I have also worked with LESS to improve code organization and maintainability through features like variables and functions.

The color applied will be based on the specificity of the selector, with ID having higher specificity than class.

• ID has higher specificity than class in CSS

• Color applied will be based on the selector with higher specificity

• Example: If ID selector has color red and class selector has color blue, the color applied will be red

I have worked on various projects including developing web applications, implementing machine learning algorithms, and optimizing database performance.

• Developed a web application using React.js and Node.js for a client in the e-commerce industry

• Implemented machine learning algorithms for predictive analytics in a healthcare project

• Optimized database performance by fine-tuning queries and indexing strategies