8 Javascript quiz that may confuse you

Originally published on Pitayan | 8 Javascript quiz that may confuse you

These days, I was preparing a small game for our team’s tech workshop. Thought it’d be a good opportunity of introducing the some fundamental and tricky stuffs around JavaScript. So I made 8 quiz to our team members. And hope they could solve them within 15 min. Eventually, it took all of them over 20 minutes to complete and most of them could solve 4-5 questions correctly.

You can take it as just a small test, each quiz has answer attached to the end of the code. Try to answer them first and then look at the answers. Good luck.

#What do these console.log print out?

#No. 1 – Doctor Pavlov has a dog

function Animal(){ 
  this.type = "animal"
}

function Dog(){ 
  this.name = "dog"
}

Dog.prototype = new Animal()

var PavlovPet = new Dog(); 

console.log(PavlovPet. __proto__ === Dog.prototype)
console.log(Dog.prototype. __proto__ === Animal.prototype)

Answer for #1

#No. 2 – Be careful with the “sort”

var arr = [5, 22, 14, 9];

console.log(arr.sort());

Answer for #2

#No. 3 – Closure and event loop

for (var i = 0; i < 3; i++) {
  const log = () => {
    console.log(i)
  }
  setTimeout(log, 100)
}

Answer for #3

#No. 4 – There’s indentation

function createNewArray(item) {
  return
    [item]
}

console.log(createNewArray(0))

Answer for #4

#No. 5 – What’s inside the “numbers”

const length = 4
const numbers = []
for (var i = 0; i < length; i++);{
  numbers.push(i + 1)
}

console.log(numbers)

Answer for #5

#No. 6 – No length

const clothes = ['shirt', 'socks', 'jacket', 'pants', 'hat']
clothes.length = 0

console.log(clothes[3])

Answer for #6

#No. 7 – Variable went crazy

var a = 1
function output () {
    console.log(a)
    var a = 2
    console.log(a)
}
console.log(a)
output()
console.log(a)

Answer for #7

#No. 8 – There’s an accidental declaration

function foo() {
    let a = b = 0
    a++
    return a
}

foo()
console.log(typeof a)
console.log(typeof b)

Answer for #8

#In the end

Thanks so much for reading! Have you got them all correct?