JavaScript Quiz

I will post some questions in JavaScript from today onwards share your own solutions without running these code on your console.

1. null === undefined

2. null == undefined

3. 2+"4"

4. 2-"3"

5. ""+2

6. +"2"

Comments

[K]

Got 3. and 5. wrong, haha.

I supposed that the first operand would decide which implementation of + would be used, but I guess the rule is: string wins :D

[K]

Both convert the number to string and do a string concatination, even in one the number is the first operand and in the other the string is the first operand.

[K]

Ah, yes.

I was talking about 3 and 5 :D

[Sai gowtham]

Oh i thought it was 5 and 6.
yeah 3 and 5 are Strings😁

[Rezwan Hossain]

1. false
2. true(sure)
3. "24." (not sure)
4. "-1." (maybe)
5. "2" (sure)
6. ????

[Quentin Sonrel]

1. false
2. true
3. "24"
4. -1
5. "2"
6. 2

Looking forward for the next questions 😀

[Shreyas Minocha]

1. false
2. true
3. "24"
4. -1
5. "2"
6. true

Not sure about some of these.

Edit: Got five right!

[Antoine Mesnil]

false
true
"24"
-1
"2"
error ?

Tested it, only have one wrong

[Sai gowtham]

good try

[Antony Garand]

Syntax error on 3 and 4, beware of trailing periods!

Edit: OP removed the trailing periods!

[Kauress]

1. false [checking for type of data and value of data]
2. true [because both are of the same type i.e. falsy]
3. "24" [ coercion rules, concatenation takes place because of + operator]
4. -1 [ -1, subtraction takes place as - operator is used on numbers not on strings]
5. "2" [ again string concatenation}
6. Not sure, tell us!

[˗ˏˋ Seye Kuyinuˊˎ˗‏]

6 uses + as a short form for type conversion

[ItsASine (Kayla)]

Without looking:

'1. null === undefined: ' + false;
'2. null == undefined: ' + true;
'3. 2+"4": ' + '24';
'4. 2-"3": ' + -1;
'5. ""+2: ' + '2';
'6. +"2": ' + 2;

I love these! I even have a codepen that's kind of like this

[ItsASine (Kayla)]

Oh, yeah, I know my weird Javascript math 🎉

1 and 2 I know because of work since null and undefined can be a pain when testing.

3 is string concatination with 2 being made a string to make it magically work.

4 is making the string a number to make the math operator magically work.

5 is similar to 3 in that it's concatinating an (empty) string with a number that magically becomes a string.

6 is fun because + is the shorthand for type converting to an int.

[Oliver Kühn]

In the past I collected some strange behaviour of JavaScript:

github.com/bullgit/WAT/blob/master...

:-)

[Eljay-Adobe]

One of my favorite web-slinger questions (for fun, not for job interviews) is: can you name all 8 of the falsy things?

Here's the first falsy thing, to get you started, which is pretty much a gimme:

• false

[Casey Webb]

false
null
0
undefined
""
NaN

I'm out. What are the last 2?

[Josh Cheek]

Shoutout! I didn't get NaN

[Ken Bellows]

-NaN and -0

[Eljay-Adobe]

Here they all are. I realize that two of them will bring out the angry mob with their torches and pitchforks. But my disclaimer is that I did not write the language.

First the easy 6 falsy things:

• false
• 0
• ""
• undefined
• null
• NaN

Plus the final two falsy things, the second of which being an HTML-ism (part of the HTML specification):

• -0
• document.all