FiftyFive Technologies Full Stack Developer Interview Questions and Answers

Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope.

• Variable declarations are hoisted to the top of the function or global scope.

• Function declarations are also hoisted to the top of the function or global scope.

• However, only the declarations are hoisted, not the initializations.

Hooks in ReactJS are functions that let you use state and other React features without writing a class.

• Hooks were introduced in React 16.8 to allow functional components to have state and lifecycle methods.

• Some commonly used hooks are useState, useEffect, useContext, and useReducer.

• Hooks allow you to reuse stateful logic across multiple components without changing the component hierarchy.

• Example: useState hook allows y...read more

Closures in JavaScript allow functions to access variables from an outer function even after the outer function has finished executing.

• Closures are created whenever a function is defined within another function.

• Inner functions have access to the outer function's variables even after the outer function has returned.

• Closures can be used to create private variables and functions in JavaScript.

• Example: function outerFuncti...read more

Higher order functions in JavaScript are functions that can take other functions as arguments or return functions as output.

• Higher order functions can be used to create more flexible and reusable code.

• Examples include functions like map, filter, and reduce in JavaScript.

• Higher order functions can help with tasks like data manipulation, event handling, and asynchronous programming.

Map and reduce functions are higher-order functions in JavaScript used to transform and aggregate data in arrays.

• Map function applies a function to each element in an array and returns a new array with the results.

• Reduce function applies a function to each element in an array, accumulating a single value.

• Example: const numbers = [1, 2, 3]; const doubled = numbers.map(num => num * 2); const sum = numbers.reduce((acc, cu...read more

Enums in TypeScript allow developers to define a set of named constants.

• Define an enum using the 'enum' keyword followed by the enum name and list of constants

• Access enum values using the enum name followed by a dot and the constant name

• Enums can have string or numeric values, and can also be used as types

Event loop in JavaScript manages asynchronous operations by executing callback functions in a queue.

• Event loop is responsible for handling asynchronous operations in JavaScript.

• It allows non-blocking I/O operations by executing callback functions in a queue.

• Event loop continuously checks the call stack and the callback queue to determine which function to execute next.

Use the sort() method in JavaScript to sort an array of strings.

• Use the sort() method with a compare function to sort the array alphabetically.

• Example: array.sort((a, b) => a.localeCompare(b));