Cognizant React Js Frontend Developer Interview Questions, Process, and Tips

Online Hackathon test was taken.

Q1. Tell Me About Yourself.
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Q2. Tell me about your roles and responsibilities in your current project.
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Q3. How we implement SSR in React.
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Q4. How can we change our project in production mode from development mode.
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Q5. What is lazy loading and how we can implement in our project.
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Q6. What is react routing and how it is different from other conventional routing methods.
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Q1. What is Redux ? How we are using it in real time
Ans. 
Redux is a predictable state container for JavaScript apps.
• Redux is a state management library for JavaScript applications.

• It helps in managing the state of the application in a predictable way.

• Redux stores the entire state of the application in a single immutable object.

• Actions are dispatched to update the state, and reducers specify how the state changes in response to actions.

• Redux is commonly used with React to man...read more
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Q2. What is Virtual Dom ? and its work in reactjs
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Virtual DOM is a lightweight copy of the actual DOM in memory, used by React to improve performance by minimizing actual DOM manipulations.
• Virtual DOM is a concept where a lightweight copy of the actual DOM is kept in memory.

• React uses Virtual DOM to improve performance by minimizing actual DOM manipulations.

• When state changes in a React component, a new Virtual DOM representation is created and compared with the previ...read more
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Q3. What is difference in usememo and react.memo
Ans. 
useMemo is used for memoizing expensive calculations, while React.memo is used for memoizing functional components.
• useMemo is a hook used to memoize expensive calculations and only recompute the value when the dependencies change.

• React.memo is a higher order component used to memoize functional components and prevent unnecessary re-renders.

• useMemo is typically used for optimizing performance by caching values, while Re...read more
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Q4. Difference between map and forEach ?
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map returns a new array with modified elements, forEach does not return anything and just iterates over the array.
• map returns a new array with the results of calling a provided function on every element in the array.

• forEach executes a provided function once for each array element without returning anything.

• Example: const numbers = [1, 2, 3]; const doubled = numbers.map(num => num * 2); // doubled will be [2, 4, 6]; num...read more
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Q5. Find Duplicacy Array
Ans. 
Find duplicates in an array of strings
• Iterate through the array and use a hash map to keep track of the frequency of each element

• If an element is already in the hash map, it is a duplicate
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Q6. What is Currying function ?
Ans. 
Currying is a technique in functional programming where a function with multiple arguments is transformed into a sequence of functions, each taking a single argument.
• Currying helps in creating reusable functions and improving code readability.

• It allows partial application of functions, where some arguments are fixed and others are left to be provided later.

• Example: const add = (a) => (b) => a + b; add(2)(3) will return
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Q1. Write HOC Component ?
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A Higher Order Component (HOC) is a function that takes a component and returns a new component with additional functionality.
• HOCs are used to share code between components, add additional features, or modify behavior.

• They are commonly used for tasks like authentication, logging, and data fetching.

• Example: const withAuth = (WrappedComponent) => { return class extends React.Component { render() { return
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Q2. Write custom hook ?
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A custom hook is a reusable function that allows you to extract component logic into a separate function.
• Custom hooks start with 'use' keyword.

• Custom hooks can call other hooks if needed.

• Custom hooks can be shared and reused across multiple components.
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Q3. Write closure function
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A closure function is a function that has access to its own scope, as well as the outer scope in which it was defined.
• A closure function can access variables from its outer scope even after the outer function has finished executing.

• Closures are commonly used to create private variables in JavaScript.

• Example: function outerFunction() { let outerVar = 'I am outer'; return function innerFunction() { console.log(outerVar);...read more
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