Top front end developer interview questions

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Real interview questions from top companies for Front end developer. Includes theoretical concepts and coding problems.

What is the difference between var, let, and const in JavaScript?

What is a closure in JavaScript?

What is the difference between null and undefined in JavaScript?

What is a promise in JavaScript?

What is the difference between synchronous and asynchronous code in JavaScript?

What is a callback function in JavaScript?

What is the purpose of the 'this' keyword in JavaScript?

What is a higher-order function in JavaScript?

What is the difference between a function declaration and a function expression in JavaScript?

What is a JavaScript module?

What is the purpose of the 'use strict' directive in JavaScript?

Write a JavaScript function that takes a string as input and returns the string with all vowels removed.

function removeVowels(str) {
  return str.replace(/[aeiou]/gi, '');
}

Write a JavaScript function that takes an array of numbers as input and returns the sum of all numbers in the array.

function sumNumbers(arr) {
  return arr.reduce((a, b) => a + b, 0);
}

Write a JavaScript function that takes a string as input and returns the string with all characters reversed.

function reverseString(str) {
  return str.split('').reverse().join('');
}

Write a JavaScript function that takes an object as input and returns a new object with all properties that have a value of null or undefined removed.

function removeNullProperties(obj) {
  return Object.fromEntries(
    Object.entries(obj).filter(
      ([key, value]) => value !== null && value !== undefined
    )
  );
}

Write a JavaScript function that takes an array of objects as input and returns a new array with all objects that have a specific property removed.

function removeObjectsWithProperty(arr, prop) {
  return arr.filter((obj) => !Object.prototype.hasOwnProperty.call(obj, prop));
}