Walstar Technologies Front end Developer Interview Questions and Answers

Q1. Let var const in JavaScript
Ans. 
var and const are used to declare variables in JavaScript, with var being mutable and const being immutable.
• var is used to declare variables that can be reassigned and updated

• const is used to declare variables that cannot be reassigned or updated

• let is another keyword used for declaring variables, similar to var but with block scope
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Q2. Error boundary and how to handle
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Error boundary is a React component that catches JavaScript errors anywhere in a component tree and logs those errors.
• Error boundaries are React components that catch JavaScript errors in their child component tree.

• They are used to prevent the entire UI from crashing due to a single error.

• Error boundaries work like a JavaScript catch {} block, but for components.

• They are defined using componentDidCatch lifecycle method
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Q3. Event.bind and event.property
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Q4. Use of never in typescript
Ans. 
The 'never' type in TypeScript represents a value that will never occur.
• Used to indicate that a function will not return a value

• Commonly used in union types to exclude certain values

• Helps catch potential errors at compile time
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Q5. What hooks you have used
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I have used React hooks such as useState, useEffect, useContext, and useRef in my projects.
• useState

• useEffect

• useContext

• useRef
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Q6. What is difference between use reducer and use state
Ans. 
useReducer is preferred for managing complex state logic, while useState is simpler for basic state management.
• useReducer is more suitable for managing complex state logic and multiple state values

• useState is simpler and more straightforward for basic state management with a single value

• useReducer allows for more organized and centralized state updates through actions and reducers

• useState is commonly used for simple co
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Q7. Why we use state and props
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Q8. How you will pass data from parent to child
Ans. 
Data can be passed from parent to child components in React using props.
• Pass data as props from parent component to child component

• Use state management libraries like Redux or Context API for complex data sharing

• Use callback functions to pass data from child to parent components
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Q9. Write your own custom hook
Ans. 
Custom hook to fetch data from an API
• Create a function that uses the useState and useEffect hooks

• Use the fetch API to make a request to the desired endpoint

• Return the fetched data and loading state in an array
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Q10. Explain map filter and reduce functions
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Map, filter, and reduce are higher-order functions in JavaScript used to manipulate arrays.
• Map: Transforms each element in an array and returns a new array with the transformed elements.

• Example: [1, 2, 3].map(num => num * 2) returns [2, 4, 6].

• Filter: Returns a new array with elements that pass a certain condition.

• Example: [1, 2, 3].filter(num => num > 1) returns [2, 3].

• Reduce: Applies a function against an accumulator ...read more
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Q11. How you can clone an object
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To clone an object in JavaScript, you can use the spread operator or Object.assign() method.
• Use the spread operator to create a shallow copy of an object: const clonedObj = { ...originalObj };

• Use Object.assign() method to create a shallow copy of an object: const clonedObj = Object.assign({}, originalObj);

• For deep cloning, you can use libraries like Lodash or write a custom function to recursively clone nested objects.
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Q12. What are the three stages of event propagation and how to handle it
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Event propagation consists of three stages: capturing, target, and bubbling.
• Capturing phase: Events are captured from the outermost element to the target element.

• Target phase: Event reaches the target element where the event originated.

• Bubbling phase: Events bubble up from the target element to the outermost element.
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Q13. How to handle errors in your react application
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Errors in a React application can be handled by using error boundaries, try-catch blocks, and displaying error messages to users.
• Use error boundaries to catch errors in components and display a fallback UI

• Wrap code that may throw errors in try-catch blocks to handle exceptions

• Use libraries like React Error Boundary to easily implement error handling

• Display error messages to users to inform them about the issue and poss
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Q14. Write code to call fake api and display the title where category is “some category “
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Q1. Basics of react and JavaScript
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It was easy not that hard

Coding question were on medium level

Q1. Be prepared for project question
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Q1. How to handle state in functional components.
Ans. 
State in functional components can be managed using the useState hook in React.
• Use the useState hook to declare state variables in functional components.

• useState returns an array with the current state value and a function to update that value.

• Example: const [count, setCount] = useState(0);

• State variables should be immutable, so always use the setter function to update them.
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Q2. What is event loop in javascript.
Ans. 
Event loop in JavaScript is responsible for handling asynchronous operations by executing callback functions in a non-blocking way.
• Event loop is a mechanism that allows JavaScript to perform non-blocking operations.

• It continuously checks the call stack and the callback queue to see if there are any functions that need to be executed.

• If the call stack is empty, it takes the first function from the callback queue and pus...read more
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Q3. What is hosting in Javascript
Ans. 
Hosting in JavaScript refers to the process of declaring a variable or function before it is used in the code.
• Hosting allows you to use variables and functions before they are declared in the code.

• Variables are hoisted to the top of their scope, while functions are fully hoisted.

• Example: console.log(myVar); var myVar = 10; This will not throw an error because 'myVar' is hoisted to the top of the scope.
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Q1. How to comment in javascript
Ans. 
Comments in JavaScript are used to explain the code and are not executed by the browser.
• Use // for single line comments

• Use /* */ for multi-line comments

• Comments help other developers understand your code
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Q2. Write code of async-await
Ans. 
Async-await is a feature in JavaScript that allows for asynchronous programming using promises.
• Use the 'async' keyword before a function to make it asynchronous

• Use the 'await' keyword inside an async function to wait for a promise to resolve

• Async-await simplifies asynchronous code and makes it easier to read and maintain
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Find reverse string using array

Q1. What are Routing Guards?
Ans. 
Routing guards are used in Angular to control access to certain routes based on certain conditions.
• Routing guards are used to protect routes in Angular applications.

• They can be used to control access based on authentication status, user roles, etc.

• There are different types of routing guards like CanActivate, CanActivateChild, CanDeactivate, CanLoad.

• Example: CanActivate guard can be used to check if a user is authentica
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Q1. Difference between foreach and map
Ans. 
foreach is used to iterate over an array without returning a new array, while map creates a new array by applying a function to each element.
• foreach does not return a new array, while map does

• foreach does not modify the original array, while map creates a new array

• foreach is used for iterating over elements, while map is used for transforming elements

• Example: foreach - array.forEach(item => console.log(item)), map - ar
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Q2. Explain rxjs operators
Ans. 
RxJS operators are functions that enable complex asynchronous operations and data manipulation in reactive programming.
• RxJS operators are used to transform, filter, combine, and create observables.

• Operators can be categorized into creation operators, transformation operators, filtering operators, combination operators, and utility operators.

• Examples of operators include map, filter, mergeMap, switchMap, debounceTime, a
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