FiftyFive Technologies Full Stack Developer Interview Questions and Answers

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, curr) => acc + curr, 0);

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.

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 you to add state to functional components.

• Example: useEffec...read more

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));

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 outerFunction() { let outerVar = 'I am outer'; function innerFunction...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

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.