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There is a convention to prefix boolean variables and function names with "is" or "has". You know, something like isLoggedIn, hasAccess or things like that.

But throughout my career I have seen and written code where this convention was just thrown out the window. So let's check out some of these edge cases.

As with all rules, there are exceptions and it might be better to go with that rather than enforcing a convention.

Boolean that verifies that every case is true

const XXX = users.every(user => user.isActive)

XXX will only be true if every user is active. How could we name the variable?

variable	Any good?	Reason
isUsersLoggedIn	🤨	Grammatically incorrect
areUsersLoggedIn	🤔	Custom prefix
isEveryUserLoggedIn	👍	Fits with `Array.prototype.every`
isEachUserLoggedIn	🥰	Comes off more natural than "every" (depends)

Boolean that verifies that one of many cases is true

const XXX = users.some(user => user.isActive)

XXX will only be true if at least one user is active.

variable	Any Good?	Reason
isUsersActive	🙁	Grammatically incorrect & ambiguous
isAtLeastOneUserActive	😵	Too wordy
isOneUserActive	🤥	Lie. This could imply that there is only one user active. Avoid confusion!!!
isSomeUserActive	👍	Fits with `Array.prototype.some`
isAnyUserActive	🤗	Comes off more natural than "some" (depends)

Avoid custom prefixes

We covered this in one of the examples before already, but there are more...

variable	Any good?	Reason
wasPaidFor	🤔	Custom prefix
areBillsPaidFor	🤔	Custom prefix
hadHaveHadBeenPaidFor	😶	Ok, I'm just joking at this point
isPaidFor	😊

Affirmative names

variable	Any good?	Reason
isDisabled	🧐	Negative
isNotActive	🤯	Just imagine `!isNotActive`
hasNoBillingAddress	😞	No need for "no"
isEnabled / isActive / hasBillingAddress	😁	And use it like this `!isActive` to get the negative

The problem with negative variable names becomes most apparent when you have something like this

if (!account.isDisabled) {
  // ...
}

Just see how much easier this reads

if (account.isEnabled) {
  // ...
}

Finally let's take a look at a more complex example.

const isAnyUserOffline = users.some(user => !user.isOnline)

if (isAnyUserOffline) {
  // ...
}

While this works, because of the combination of some and !, it just takes a little more brain power to process this code. An alternative would be:

const isEveryUserOnline = users.every(user => user.isOnline)

if (!isEveryUserOnline) {
  // ...
}

It behaves the same and as long as the data set is small enough I would not worry about the small performance impact.

I am sure there is a lot I missed, but I think these are some of the more common cases.

If this article helped you, I have a lot more tips on simplifying writing software here.

Tips on naming boolean variables - Cleaner Code

Boolean that verifies that every case is true

Boolean that verifies that one of many cases is true

Avoid custom prefixes

Affirmative names