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())
What is the output? 👇
- A)
code__oz
and['js', 'ts', 'vuejs', 'nodejs']
- B)
undefined
andundefined
- C)
code__oz
andundefined
- D)
undefined
and['js', 'ts', 'vuejs', 'nodejs']
.
..
...
....
.....
......
.......
.......
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)
What is the output? 👇
- A)
undefined
- B)
Bye
- C)
Hello
- D)
ReferenceError
.
..
...
....
.....
......
.......
.......
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)
What is the output? 👇
- A)
1 1 2
- B)
1 2 2
- C)
0 1 2
- D)
0 2 2
.
..
...
....
.....
......
.......
.......
D -> The postfix unary operator ++
:
- Returns the value (this returns
0
) - Increments the value (number is now
1
)
The prefix unary operator ++
:
- Increments the value (number is now
2
) - Returns the value (this returns
2
)
This returns 0 2 2
.
4
function sum(a, b) {
return a + b
}
sum(2, '5')
What is the output? 👇
- A)
TypeError
- B)
NaN
- C)
"25"
- D)
7
.
..
...
....
.....
......
.......
.......
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)
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? 👇
.
..
...
....
.....
......
.......
.......
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!
🎁 You can get my new book Underrated skills in javascript, make the difference
for FREE if you follow me on Twitter and MP me 😁
Or get it HERE
☕️ You can SUPPORT MY WORKS 🙏
🏃♂️ You can follow me on 👇
🕊 Twitter : https://twitter.com/code__oz
👨💻 Github: https://github.com/Code-Oz
And you can mark 🔖 this article!
Top comments (25)
got 2/5 :,(
3/5 !
4/5 :)
Last question makes me disappointed
it's a good score !
4/5, thanks for this refresher and letting me know that I need to do some reading up!
Well done! It's a great score!
3/5.
Thanx for 5th ques, i was unaware ....
well done and thanks dude ! 💪
3/5
Nice Try !
DOH!
I got 3/5 :,(
It's a great score! You will have more next time ;)
5/5 Thx. Good questions
Nice! And thank you 😁
4/5. Your article is interesting ☺️
Well done! And thanks a lot 😁