Michael Z

Posted on Oct 3, 2019 • Updated on Jan 9, 2022 • Originally published at michaelzanggl.com

Tips on naming boolean variables - Cleaner Code

#codequality #refactorit

Originally posted at michaelzanggl.com. Subscribe to my newsletter to never miss out on new content.

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.

Top comments (51)

Stepan Stulov • Dec 18 '19 • Edited

This whole naming of booleans is one of the simplest yet most misunderstood conventions in programming.

You seem to be a proponent of naming booleans as affirmative statements, yet you name your booleans as questions. This seems contradictory to me.

isEveryUserOnline? Is he? I don't know, maybe? Are you asking me? Or is anyone standing behind me? Why is code talking to me and making me decide? Code is a set of commands. It answers questions. It doesn't ask them.

Purely linguistically, you don't say "If am I a developer". You say "If I am a developer".

Your isEveryUserOnline variable should be named everyUserIsOnline or allUsersAreOnline. This would truly be affirmative, according to your own standard. This will also read well in English and go well with order of words when using dot notation. Compare:

// Same order, erase the dot and you got yourself a variable name.
bool userIsActive = user.isActive;

// Order changed, statement suddenly became a question.
// Also have to bother about moving words around.
bool isUserActive = user.IsActive;

The only standard you really need for booleans is an affirmative statement that evaluates to either true or false. That's it. Hello, Propositional Calculus. Is, are, has, was, did, will, should, must, can: all just flavors.

As for prefixing for the sake of prefixing, I thought that was called Hungarian notation and is more or less dead, with a few relics still roaming the Earth.

Hope this helps,
Cheers

A-ZC-Lau • Apr 28 '21 • Edited

isEveryUserOnline? Is he? I don't know, maybe? Are you asking me? Or is anyone standing behind me? Why is code talking to me and making me decide? Code is a set of commands. It answers questions. It doesn't ask them.

Seems very pedantic. The word is isn't asking you, it's invoking a question with a binary answer.

userIsActive is a statement. It makes it sound like a constant.

Take for example "Is it 5 o'clock" would invoke a yes/no answer in your mind immediately. If your brain suddenly thinks that the computer is talking to you, rather than you realizing that the variable is actually saving a boolean, it's a problem between chair and keyboard.

Conversely, with your format, "It is 5 o'clock" would be a statement. You don't answer a statement, which makes it seem like a constant.

In fact, I would argue that statements are invocation of action. Because you wouldn't have a statement of "It is 5 o'clock" and then do nothing with it. So the name userIsActive would be a function i.e. userIsActive(), which you would use as in

if (isUserActive) { 
    userIsActive()
}

Stepan Stulov • May 17 '21 • Edited

For invocation of actions in the imperative programming paradigm, with which you (arguably) unbeknownst to yourself operate, imperative mood of verbs is conventionally used. This is what gave imperative programming paradigm its very name.

if (userIsActive)
    SetUserActive(false); // Imperative mood of the word "set"

PS: In an educated and intelligent community such as ours we do not call people "a problem between the chair and the keyboard" just because we disagree. Disagree one may. Insult one may not. Assuming education and intelligence are there in the first place, of course.

Davide de Paolis • Sep 7 '20 • Edited

absoulutely agree. i understand the need for the convention, since ( expecially at the beginning of your career) you are able to immediatly find or recogninze a boolean variable by the fact that starts with is or has, but was never bought into this.
exactly for the reason you mentioned,

is it a question? are you asking me? i don't know, you should tell me!

and because of the many exceptions that make some variables seriously grammatically terrible. I found this post because I was looking for alternatives or way of telling in a Pullrequest that isUserAlreadyExist is a complete NOPE for me...

imho, dimply use conventions when it makes sense, ( possiblly in thex affermative format - like useIsActive - which in my case would become a more natural userAlreadyExists)

Konstantin • Jan 16 '21 • Edited

What about the point that no code ask you but you have asked the data about something and store answer in variable with the same name?

Rafael Pereira • Jan 20 '22

Purely linguistically, you don't say "If am I a developer". You say "If I am a developer".

In english, a sentence beginning with a verb is a question most of the time. So for foreigners, it's a no brainer a variable starting with a questioning verb is a boolean.

I get it that native english speakers don't really talk the way the grammar is technically but this is how non native people learn the language, by learning and studying grammar first. And reading is different than speaking. We're reading code every day, not speaking. To simply ignore it because of use is a cultural thing and not really in the rules of the language.

Just my thoughts and point of view, from other perspective, to add to the conversation. But in the end of the day, it's good to be consistent. That's all.

niemeier23 • Mar 18 '21

I created an account here just to <3 this comment.

It's not important at all that the auxiliary verb (is, has, was, etc) is a prefix, or not. It's not important that it be singular, and not plural. It's not important what temporal tense it's in.

It's about expressing a boolean value so that any English reading person could understand it, even if s/he doesn't know any programming principles. Make it literal and readable.

everyUserIsActive
someUsersAreActive
wasSuccessfullyUpdated
user.isAdmin

The variable should not beg the question, "what does this even mean?" or "what is this referring to?" It should be perfectly clear by simply reading it.

My other boolean pet peeve is this:

if($user->isAdmin) {
return true;
}
else {
return false;
}

Why not:
return $user->isAdmin;
?

Lee Raulin • Oct 20 '21

I've been wasting more time than I should agonizing over this, but I agree with Stephan. I prefer everyUserIsOnline over isEveryUserOnline. That way I can write: "if (everyUserIsOnline)" and it reads like an English sentence. Couldn't be more clear what's happening.

I was tempted to go along with the original post, but when trying to actually use something like, "if (isEveryUserOnline)"... Just... No. Just feels wrong. Is every user online? I dunno. "If is every" wtf does that even mean? And you rule out other options for being ungrammatical?

Yes, I'm a programmer and know how booleans work, I could understand if it was named oaentuh0296eoau, especially with the help of VSCode Intellisense, so then why bother with any of this? Seems to me the more it reads like an actual sentence, the more clear it is what's going on.

And why insist on having is as a prefix? For the sake of adhering to some pseudo-Hungarian notation style that we use nowhere else? At the expense of clarity? I don't see the point.

Robert Concepcion III • Apr 16 '20 • Edited

I mostly agree with you that code readability should be one of the #1 priorities, but at the tend of the day it depends on the context -- also the whole "when in rome" thing.

I'll give you just another perspective: in my situation, I don't use Typescript at my every-day-work, so things are weakly typed, and the IDE auto-prediction works relatively well with VSCode.

Because of that, using is/has/should gives several benefits (magnified in a weakly typed language):
-> auto-prediction is actually very helpful when there's no ESDoc annotation written in common code.
-> consistency, and knowing immediately what something is (though I'd agree and enjoy to work on more other-people's code which is thought out to read-well and flow well as you seem to encourage). There's an aspect of things where if you learn to speed read, the effect when you're glancing over words implies that you catch the first-and-last-part-of-words.
-> when interfacing APIs/other things, getters/setters are easy to automate code with (at least for JS/Ruby), and it's easy to write linter rules on weakly typed languages.

Volodymyr Liutkin • Aug 19 '23

Thank you, exactly how I’ve been feeling. Affirmative names are also great at negating: !user.online, !sessionActive, !changesSaved.

Stepan Stulov • Aug 23 '23

Don't forget the verb "to be": user.isOnline, sessionIsActive, changesAre/WereSaved.

Bryn Dyment • Apr 8 '22

I would say that the variable name is indeed a question and the variable value is the answer to said question.

Adam Crockett 🌀 • Oct 3 '19

isGrammaticallyIncorrect

I think this is cultural, I'm a dyslexic programmer from the south west of englind, a place with its own dilect, where "dibber" and "doofer" exist to fill in the names of things we can't remember the name of. A variable assistant if you will. I am fine with the first of each. What I am not fine with is this program not working.

Carlos Trapet • Oct 3 '19

if (!hasDibberInDoofer)

I love it!

Adam Crockett 🌀 • Oct 3 '19

Shall I use it in a sentence.

Wife of mine: "pass me the doofer"

Me: 🥺

Wife of mine: "you know that doofer over there" (she doesn't point)

Me: bring an assortment of just about anything in reach.

Wife of mine: "for god sake, do I have to do everything myself"

Me: 😤🤦‍♂️🚶

So there you go, never visit Bristol, it's confusing just like naming variables.

Anita Graham • Jul 30 '20

I am from the South West of Australia (and not dyslexic, to the point of pedantry), and we would say "doover" for that sort of placeholder word. (Mum had Irish grandparents on all sides, so I assumed it came from there).

The full name of a doover is a "dooverlacky". Mentally I associate "doover" with "horse doover", which is a variation of "hors d'oeuvres", so not at all connected.

Adam Crockett 🌀 • Jul 30 '20

Woah this wouldn't surprise me if doofer is one and the same thing. Today I learned 😁

Adam Crockett 🌀 • Oct 3 '19

You my friend have invented the new foo bar!

Yuval • Dec 19 '22

Should replace foo and bar :)

Sophie The Lionhart • Oct 3 '19

Nice! I normally don't find anything valuable in a lot of the more 'basic' articles of advice for newer devs anymore as I've been a dev for over 5 years, but sometimes the right way to name booleans with an 'is', 'has', or whatever eludes me. This is a great little bit of advice and guide! Thanks for the write up and keep up the good work!

Jarod Brennfleck • Oct 5 '19

I don't think it actually should matter how your variable names are prefixed. Particularly with "custom prefixes" if it sounds more correct for the usage of the variable, then use it!

If the boolean is a confirmatory boolean and is reset when accessed, the by all means, use "was": enter.wasKeyPressed.

Just my 2¢. Otherwise, a fun read! 🤙

Christian • Dec 1 '20

enter.keyWasPressed

Michael Z • Oct 5 '19

Yes that's true, I added it to the article that going with an exception is better than enforcing a convention where it makes sense.

Volodymyr Liutkin • Aug 19 '23

enter.pressed

Michael Z • Oct 4 '19 • Edited

That was not the intention of this article and I am sorry you feel that way. I wanted to share tips for something I personally struggled with in the past and know others have too.

I try not to be picky in code review and don't bother with the things (grammar, spaces, semicolons, commas, etc.) you mentioned.
If a name is confusing I might leave a comment with a suggestion, but by no way enforce any of this stuff, it's all subjective.

Matthieu L. • Dec 12 '19

Great article, thanks !
Question, how do you name boolean getters ?
I've seen people using booleans like "empty" and getters like "isEmpty()", but I prefer having is/has prefixes for booleans as you say.
I use getters like "getIsEmpty()" for an "isEmpty" boolean, but many people find it akward..

Stepan Stulov • Dec 18 '19

Many people do but stand your ground, it's good.

Christian • Dec 1 '20 • Edited

I prefer to leave verbs for functions, such as getters.

let empty = true;

const isEmpty = () => empty;
const getEmpty = () => empty;

Paddy3118 • Oct 4 '19

Since it is a group of things that may be active, I'd use allActive, anyActive, noneActive, oneActive,...

Paddy3118 • Oct 4 '19

You can also use gt, ge, lt, le, eq then a number as prefixes for greater-than, greater-than-or-equal, less-than, less-than-or-equal, equal

Something like:

le3Active = activeCount(active) <= 3
gt4Active = activeCount(active) > 4

Christian • Dec 1 '20

oof. I read this as "Le Three Active"

Luigi Minardi • Oct 5 '19

isTwoLoggedIn?
areTwoLoggedIn?
isThereTwoLoggedIn?

What should it be? Any other option?

Michael Z • Oct 5 '19

That's a tough one.
What came to my mind was also
isPairLoggedIn
isPairOfUsersLoggedIn

Never ran into this case before though :D

David Latty • Sep 29 '20

Horrid

Stepan Stulov • Dec 18 '19 • Edited

Two of whom? :)

twoUsersAreLoggedIn

Marko Vujanic • Jul 13 '22 • Edited

You changed my mind with

Code is set of comands, it dosent ask questions it answers them.

Following that logic, you don't really need is as prefix, and naming of boolean follows the logic nicelly, much more readable, becouse I tryed changing all is to 'command', suprisingly it's just much more readable and parsable in by my head.

isSendEmailFetching -> (request is made to job to send email)
sendingEmail

I wonder what do you think about using transitive verb like this?

Thank you

Stepan Stulov • Aug 12 '22

Alternatively, in passive voice, emailIsBeingSent.

David Latty • Sep 29 '20

Good stuff

Kamal • Dec 3 '20

hadHaveHadBeenPaidFor
this made me chuckle on the middle of the day, thank you :))

NikitaArgov • Dec 25 '19

Great article, thank you!

Found it, trying to find idea for naming of boolean "AreContactsShown". Name "isEachContactShown" would be weird - there are no separate contact items.

Any suggestions?

Christian • Dec 1 '20

contactsAreShown, contactsAreVisible, or create an object: contacts.visible

Michael Z • Dec 25 '19

Thanks!

Where are the contacts displayed in? You could maybe use that instead, e.g. isContactListShown

Brad • Oct 3 '19

As they say, one of the hardest things with programming is naming stuff. Great article, I'll have to re-think my naming conventions in the future now 😄