Mantra Technologies Front end Developer Interview Questions and Answers

Q1. Basics about angular
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Q2. Javascript concepts
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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
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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
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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
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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
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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. Reverse the string
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Reverse a given string
• Use built-in methods like split(), reverse(), and join() to reverse the string

• Alternatively, loop through the string from end to start and build a new reversed string
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Q1. How to handle state in functional components.
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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.
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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
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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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