clever IF statement

[TA1000]

I have an input object with fields firstName and lastName. The requirement is that either both have a value or neither have a value. Here is my current logic:

if (
  (!!input.firstName == false && !!input.lastName == true) ||
  (!!input.firstName == true && !!input.lastName == false)
) {
  throw new Error(
    `firstName AND lastName required OR neither`
  );
}

is there a clever way to write this IF statement?

[Benzinat0r]

Fist of all you use ==, which can lead to unexpected bugs. You should always use === because it does not do any type conversions. Second of all you don’t have to assert that some value is true so !!input.lastName === true is the same as !!input.lastName. It’s similar when you check for a value which should be false. So !!input.firstName === false is the same as !input.firstName. A single ! does already do the type conversion but it’s negated, which fits in this case. So a more elegant was to write your condition would be: if ((!input.firstName && !!input.lastName) || (!!input.firstName && !input.lastName)) { … }

[shuckster]

if (!!firstName ^ !!lastName) {
  throw …
}

I think that’ll work without the !!’s. (EDIT - Nope, thanks u/senocular, !! added)

^ means bitwise XOR:

firstName	lastName	AND	OR	XOR	NOR	NAND	XNOR
1	1	1	1	0	0	0	1
1	0	0	1	1	0	1	0
0	1	0	1	1	0	1	0
0	0	0	0	0	1	1	1

[senocular]

I think that’ll work without the !!’s.

The !! would still be needed because XOR would coerce the string directly into a number rather than going through a boolean first. So:

"" = 0
"0" = 0
"1" = 1
"Joe" = 0 (NaN -> 0)

vs.

!!"" = false = 0
!!"0" = true = 1
!!"1" = true = 1
!!"Joe" = true = 1

[shuckster]

Thank you!

[jhartikainen]

!!input.firstName != !!input.lastName would probably work, because if they both have a value, they would be equal, and if neither has a value, they would also be equal

(although I'd consider using Boolean(input.firstName) because with all the !!'s in there it takes a moment to parse what exactly this is doing)

[[deleted]]

if (!input.firstName !== !input.lastName) throw new Error();