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Code Oz
Code Oz

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5 Quizz explained in Javascript #1

Welcome to the first javascript quizz!

You can answer to the question and check the response with the explication!

Good luck!

1

const myself = {
  name: 'code__oz',
  skills: ['js', 'ts', 'vuejs', 'nodejs'],
  getName() {
    return this.name
  },
  getMySkills: () => this.skills,
}

console.log(myself.getName())
console.log(myself.getMySkills())
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What is the output? 👇

  • A) code__oz and ['js', 'ts', 'vuejs', 'nodejs']
  • B) undefined and undefined
  • C) code__oz and undefined
  • D) undefined and ['js', 'ts', 'vuejs', 'nodejs']

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C → We have undefined value since we are using arrow function and this in the same context, so the this keyword refers to its current surrounding scope, unlike regular functions! In a browser context, this refer to window object!

2

let toto = { message: 'Hello' }
let tutu

tutu = toto
toto.message = 'Bye'
console.log(tutu.message)
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What is the output? 👇

  • A) undefined
  • B) Bye
  • C) Hello
  • D) ReferenceError

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B → In JavaScript, all objects interact by reference when setting them equal to each other. So in this example toto and tutu share the same reference so if you change value from one, you will change the shared reference and you will indirectly change the value of the other variable.

3

let number = 0
console.log(number++)
console.log(++number)
console.log(number)
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What is the output? 👇

  • A) 1 1 2
  • B) 1 2 2
  • C) 0 1 2
  • D) 0 2 2

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D -> The postfix unary operator ++:

  1. Returns the value (this returns 0)
  2. Increments the value (number is now 1)

The prefix unary operator ++:

  1. Increments the value (number is now 2)
  2. Returns the value (this returns 2)

This returns 0 2 2.

4

function sum(a, b) {
  return a + b
}

sum(2, '5')
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What is the output? 👇

  • A) TypeError
  • B) NaN
  • C) "25"
  • D) 7

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C → JavaScript converts the number 2 into a string. It's because during the addition of a numeric type (2) and a string type ('5'), the number is treated like a string ! So we have '2' + '5' → '25'

5

setInterval(() => console.log('Hey !'), 5000)
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What does the setInterval method return in the browser? 👇

  • A) a unique id
  • B) the amount of milliseconds specified
  • C) the passed function
  • D) undefined

What is the output? 👇

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A -> It returns a unique id. This id can be used to clear that interval with the clearInterval() function.

Tell me your score in comment! 👨‍🏫


I hope you like this reading!

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Top comments (25)

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fiddlesmic profile image
FiddleSmic

got 2/5 :,(

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luffy124 profile image
Luffy-124

3/5 !

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xvarlordx profile image
Serafim

4/5 :)
Last question makes me disappointed

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codeoz profile image
Code Oz

it's a good score !

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dikvega profile image
Richard Carter

4/5, thanks for this refresher and letting me know that I need to do some reading up!

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codeoz profile image
Code Oz

Well done! It's a great score!

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rahulydav profile image
rahul-ydav

3/5.
Thanx for 5th ques, i was unaware ....

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codeoz profile image
Code Oz

well done and thanks dude ! 💪

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someone_49 profile image
SomeOne_49

3/5

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codeoz profile image
Code Oz

Nice Try !

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invernomutogit profile image
Alessandro Piconi

DOH!

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coderabdullahturki profile image
Abdullah-Al-Turky

I got 3/5 :,(

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codeoz profile image
Code Oz

It's a great score! You will have more next time ;)

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pavelloboda profile image
Pavel Loboda

5/5 Thx. Good questions

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codeoz profile image
Code Oz

Nice! And thank you 😁

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tranhiepnguyenhuy1999 profile image
Huy Tran

4/5. Your article is interesting ☺️

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codeoz profile image
Code Oz

Well done! And thanks a lot 😁

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mitya profile image
Dima

4/5. I should repeat postfix and prefix operators.

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codeoz profile image
Code Oz

well done ! 💪

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amisandip profile image
Sandip Mukherjee

5/5

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codeoz profile image
Code Oz

Wow well done 💪

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nehalahmed profile image
Nehal Ahmed

4/5

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codeoz profile image
Code Oz

well done Nehal!

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agnel profile image
Agnel Waghela

4/5

Got the 1st one incorrect. Missed the connection between arrow function and this keyword.

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codeoz profile image
Code Oz

well done bro !