10 Interactive JavaScript Conceptual Questions with Code Snippets for Interviews

Question 1

1Question 1 of 10

How does JavaScript handle array references when multiple variables point to the same array?

javascript

const colors = ['red', 'blue', 'green']

const favColors = colors

favColors[1] = 'purple'

console.log(colors === favColors)
console.log(colors)

Question 2

2Question 2 of 10

What happens when you use the spread operator on an object that contains nested objects?

javascript

const user = {
  name: 'Ahmed',
  email: 'ahmed@email.com',
  designation: 'Frontend Developer',
  address: { city: 'Karachi' },
}

const newUser = { ...user, designation: 'Fullstack Engineer' }

newUser.address.city = 'Lahore'

console.log(user.address.city)
console.log(newUser)

Question 3

3Question 3 of 10

How does the continue statement affect a loop's execution flow?

javascript

let num = 0

for (let i = 1; i <= 5; i++) {
  if (i % 2 === 0) continue
  num += i
}

console.log(num)

Question 4

4Question 4 of 10

How does JavaScript determine the length of sparse arrays?

javascript

const arr = [1, , 3, , 5]

arr[10] = 10

console.log(arr.length)

Question 5

5Question 5 of 10

How can arrow functions access values from their surrounding scope?

javascript

const welcome = {
name: 'Ali',
greet: function () {
  const that = this
  return () => {
    console.log('Hello, ' + that.name)
  }
},
}

const greetFunction = welcome.greet()
greetFunction()

Question 6

6Question 6 of 10

How does method overriding work in JavaScript class inheritance?

javascript

class Animal {
constructor(name) {
  this.name = name
}

speak() {
  return this.name + ' makes a noise.'
}
}

class Pet extends Animal {
constructor(name, ownerName) {
  super(name)
  this.ownerName = ownerName
}

getOwner() {
  return this.name + ' belongs to ' + this.ownerName + '.'
}
}

class Dog extends Pet {
speak() {
  return this.name + ' barks.'
}
}

const dog = new Dog('Rex', 'Alice')

console.log(dog.speak())
console.log(dog.getOwner())

Question 7

7Question 7 of 10

How do closures preserve and share private state across function calls?

javascript

const Counter = (function () {
let count = 0

return {
  increment: function () {
    count++
    return count
  },

  decrement: function () {
    count--
    return count
  },

  getCount: function () {
    return count
  },
}
})()

console.log(Counter.increment())
console.log(Counter.increment())
console.log(Counter.getCount())

Question 8

8Question 8 of 10

What happens when a Promise is resolved and then rejected immediately afterward?

javascript

let promise = new Promise((resolve, reject) => {
  resolve('Resolved')
  reject('Rejected')
})

promise
.then((result) => {
  console.log(result)
})
.catch((error) => {
  console.log(error)
})

Question 9

9Question 9 of 10

How does the logical NOT (!) operator behave when applied to truthy values?

javascript

console.log(!"Codevertiser")

Question 10

10Question 10 of 10

What is the difference between loose equality (==) and strict equality (===) when comparing primitives and objects?

javascript

let a = "Flexy UI"
let b = new String("Flexy UI")

console.log(a == b)
console.log(a === b)

10 Interactive JavaScript Conceptual Questions with Code Snippets for Interviews

10 Conceptual JavaScript Quizzes for interview prep

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