JavaScript Quiz

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

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

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

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!

I scored 4 out of 6. But if I wasn't able to run them as I went, it would be much lower.

Also, I feel like you should add "2"+4 right after 2+"4", b/c I was definitely wondering if the casting decision was based on which one was first. Eg in Ruby, + is a method call, so 2+"4" would be calling Integer#+ and "2"+4 would be calling String#+, thus the ordering implies different behaviour, even though + in math is commutative. I know that's not how JS works, but it means that I would at least be entertaining the possibility of non-commutativity.

null === undefined
// expected: false
// actual:   false
// score:    1/1

null == undefined
// expected: false... but less confidently :/
// actual:   true
// score:    1/2

2+"4"
// expected: Jesus >.< uhm... 6? If not 6, than 24, pretty sure
//           one of them gets cast, just not sure which.
// actual:   fuuuuuuck, 24 >.<
// score:    1/3

2-"3"
// expected: Based on the above, I'm really hoping it's -1
// actual:   -1
// score:    2/4

""+2
// expected: Oh fuck. uhhhh. maybe it comes in as zero, or maybe
//           it gets treated like a character string instead of
//           a number string, which maybe casts the 2 to a string
//           ...wait, yeah, it's definitely "2"!
// actual:   "2"
// score:    3/5

+"2"
// expected: Probably 2, right? I'd expect it to cast the "2" to
//           a number and then make it "positive" or something.
// actual:   2
// score:    4/6

Uhhh I love these!

I've got one for you!

Without running this in the console let me know how much is

0.1 + 0.2

Hint: it's a number bigger than the one you are thinking of right now.

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

Not sure about some of these.

Edit: Got five right!

Before running these statements:

false
true
24
-1
NaN
2

After running them

false
true
24
-1
"2"
2

4/6 😅

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

Edit: OP removed the trailing periods!

I guess :)

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

1. False
2. True
3. "24"
4. 1
5. 2
6. "2"

Well, let me run to my console to confirm that I know this nice language with weird behavior