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Persistent Systems
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I applied via LinkedIn and was interviewed in Jun 2024. There was 1 interview round.
Callbacks are functions passed as arguments to another function to be executed later
Callbacks are commonly used in event handling, asynchronous programming, and functional programming
Callbacks can be synchronous or asynchronous
Example: passing a callback function to a setTimeout() function
What people are saying about Persistent Systems
I applied via Referral and was interviewed in Nov 2024. There was 1 interview round.
posted on 14 Sep 2024
I applied via Naukri.com and was interviewed in Aug 2024. There was 1 interview round.
A closure is a function that has access to its own scope, as well as the scope in which it was defined.
A closure allows a function to access variables from its outer function even after the outer function has finished executing.
Closures are created whenever a function is defined within another function.
Example: function outerFunction() { let outerVar = 'I am outer'; return function innerFunction() { console.log(outerVa
Async/await is a feature in JavaScript that allows for asynchronous code to be written in a synchronous manner.
Async/await is built on top of promises and provides a more readable and concise way to work with asynchronous code.
The 'async' keyword is used to define a function as asynchronous, allowing it to use the 'await' keyword inside it.
When 'await' is used, it pauses the execution of the function until the promise ...
Use Set to remove duplicates from array of strings.
Create a Set from the array to automatically remove duplicates
Convert the Set back to an array if needed
Example: const arr = ['apple', 'banana', 'apple', 'orange']; const uniqueArr = [...new Set(arr)];
React DOM updates by comparing the virtual DOM with the actual DOM and only updating the necessary components.
React creates a virtual DOM to represent the UI components.
When a state or prop changes, React re-renders the virtual DOM.
React then compares the virtual DOM with the actual DOM to identify the differences.
Only the necessary components are updated in the actual DOM, minimizing performance impact.
React Hooks are functions that let you use state and other React features without writing a class.
React Hooks were introduced in React 16.8.
They allow you to use state and other React features in functional components.
Some commonly used hooks are useState, useEffect, useContext, and useRef.
Hooks make it easier to reuse logic across components.
Hooks can be used to manage component state, perform side effects, and more.
Call, bind, and apply are methods used to manipulate the value of 'this' in JavaScript functions.
Call - invokes a function with a specified 'this' value and arguments provided individually.
Bind - creates a new function that, when called, has its 'this' keyword set to the provided value.
Apply - invokes a function with a specified 'this' value and arguments provided as an array.
Redux Toolkit is a set of tools and best practices to simplify Redux development, while Redux is a predictable state container for JavaScript apps.
Redux Toolkit provides a set of tools like createSlice, createAsyncThunk, and configureStore to simplify Redux setup and reduce boilerplate code.
Redux Toolkit includes immer library for writing immutable update logic in a more convenient way.
Redux Toolkit also includes a def...
Writing a RTL test to check a button in React
Use the render and fireEvent functions from @testing-library/react
Find the button element using getByRole('button')
Simulate a click event using fireEvent.click
Assert that the button is visible and clickable
Inline and block level elements in HTML/CSS
Inline elements flow in the document in a line, without starting a new line. Examples include , , .
Block level elements start on a new line and take up the full width available. Examples include
,
Microtasks in JavaScript are tasks that are executed asynchronously and have higher priority than regular tasks.
Microtasks are scheduled to run after the current script has finished but before the browser has a chance to render.
They are often used with promises, as promise callbacks are executed as microtasks.
Microtasks are executed in the same event loop iteration as regular tasks, but before the next rendering.
Exampl...
Custom hooks are reusable functions that allow you to extract component logic into separate functions.
Custom hooks are prefixed with 'use' and can call other hooks if needed.
They can be used to share logic between components without duplicating code.
Custom hooks can be created for any kind of logic, such as fetching data, managing state, or handling side effects.
Redux is a predictable state container for JavaScript apps. It helps manage the state of an application in a centralized store.
Create a Redux store to hold the state of the application
Define actions to describe state changes
Write reducers to specify how the state changes in response to actions
Dispatch actions to update the state in the store
Connect components to the Redux store using the connect function from react-red
Redux is a predictable state container for JavaScript apps.
Actions are dispatched to the store
Reducers specify how the state changes in response to actions
Store holds the state of the application
Components can subscribe to the store to access state
posted on 4 Oct 2024
I applied via Approached by Company and was interviewed in Sep 2024. There was 1 interview round.
Debounce delays the execution of a function until after a specified time period, while throttling limits the rate at which a function can be executed.
Debounce waits for a specified time period of inactivity before executing the function, while throttling limits the rate at which the function can be called.
Debounce is useful for scenarios like search bars where you want to wait for the user to finish typing before makin...
SOAP (Simple Object Access Protocol) was used before Rest APIs for web services communication.
SOAP was a protocol for exchanging structured information in the implementation of web services.
SOAP used XML for message format and relied heavily on HTTP for communication.
SOAP was more rigid and complex compared to Rest APIs, which are more lightweight and flexible.
Examples of SOAP-based web services include Microsoft's .NE
posted on 4 May 2024
I applied via Approached by Company and was interviewed in Apr 2024. There were 3 interview rounds.
Custom hooks in React allow for reusable logic across components.
Custom hooks are functions that use React hooks internally and can be reused across multiple components.
They can encapsulate complex logic and state management, making components more modular and easier to maintain.
Example: A custom hook for fetching data from an API and handling loading and error states can be used in multiple components.
Example: A custo...
posted on 8 Mar 2024
I applied via Referral and was interviewed in Feb 2024. There was 1 interview round.
Promises in JavaScript are objects representing the eventual completion or failure of an asynchronous operation.
Promises can be in one of three states: pending, fulfilled, or rejected.
Promises can be chained using .then() to handle success and .catch() to handle errors.
Promises can be created using the Promise constructor or by using async/await syntax.
useState is used to manage state in functional components, while useEffect is used to perform side effects in functional components.
useState is used to declare state variables in functional components.
useEffect is used to perform side effects in functional components, such as data fetching, subscriptions, or manually changing the DOM.
useState does not trigger re-renders, while useEffect can be used to trigger re-render...
Callback hell is a situation where multiple nested callbacks make the code difficult to read and maintain.
Occurs when multiple asynchronous operations are nested within each other
Leads to deeply nested code structure which is hard to understand
Can be avoided by using Promises, async/await, or modularizing code
Traditional functions are defined using the function keyword, while arrow functions are defined using a concise syntax with =>.
Traditional functions are hoisted, while arrow functions are not.
Arrow functions do not have their own 'this' keyword, they inherit it from the parent scope.
Arrow functions are more concise and easier to read compared to traditional functions.
Traditional functions are better for methods in obje...
Creating a counter in React to increment and decrement a value.
Create a state variable to store the count value
Use setState to update the count value
Render the count value in the component
Add buttons to increment and decrement the count value
Program to find frequency of letters in a string
Create an object to store the frequency of each letter
Loop through the string and increment the count of each letter in the object
Convert the object into an array of strings with letter and frequency pairs
Iterate through the given string to check if the substring is present.
Iterate through the given string and check if each character matches the first character of the substring.
If a match is found, check the subsequent characters to see if they form the substring.
Return true if the entire substring is found within the given string, otherwise return false.
posted on 27 Aug 2022
I applied via Naukri.com and was interviewed before Aug 2021. There were 4 interview rounds.
I applied via Job Portal and was interviewed before Nov 2021. There were 2 interview rounds.
posted on 16 Oct 2024
I applied via Naukri.com and was interviewed in Sep 2024. There was 1 interview round.
Actual DOM represents the real structure of the web page, while Virtual DOM is a lightweight copy used for efficient updates.
Actual DOM is the real structure of the web page that is directly manipulated by the browser.
Virtual DOM is a lightweight copy of the Actual DOM that React uses for efficient updates.
Changes made to the Virtual DOM are compared with the Actual DOM, and only the differences are updated in the Actu...
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