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Please don't write confusing conditionals

Basti Ortiz on July 12, 2023

Have you ever spent more than a few seconds staring at the same line of code? How often did you find conditionals that were tricky to parse? In thi...

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Marc-Daniel DALEBA • Jul 12 '23

You are right. ヽ(・∀・)ﾉ
But in general it's better to write this instead:

if (!(!(!(!(!(!(!(!(isAllowed))))))))) {
    doSuccess();
}

(￣ω￣)

Basti Ortiz • Jul 12 '23

Ah yes... a glorious piece of code right there. 🤣

Dipendra Bhardwaj • Jul 13 '23

Ye kya harkat hai

lionel-rowe • Jul 13 '23

Affirmative is a good rule of thumb, but I think in some cases, such as HTML's disabled, it makes more sense in the negative, as the usual assumption is that an element is enabled. Which is clearer in intent?

<!-- "negative" naming convention -->
<input name="username">
<input name="password">
<button disabled title="Enter the username and password first!">Submit</button>

<!-- "positive" naming convention -->
<input enabled name="username">
<input enabled name="password">
<button title="Enter the username and password first!">Submit</button>

BTW here's a handy higher-order function when you want to convert a boolean-returning function into its opposite:

function not<T>(fn: (arg: T) => boolean) {
    return (arg: T) => !fn(arg)
}

Usage:

function isOdd(n: bigint) {
    return Boolean(n % 2n)
}

const isEven = not(isOdd)
const nums = [1n, 2n, 3n, 4n]
const odds = nums.filter(isOdd) // [1n, 3n]
const evens = nums.filter(isEven) // [2n, 4n]

Dimitrios Kechagias • Jul 14 '23

Maybe it's time for js to add the "unless" statement that Perl (and Ruby) has? We use a lot of Perl and usually our junior developers come from a javascript background, and the unless statement is one of the things they instantly like.

unless ($isUser && $isGuest) {
    doSomething();
}

Or if you don't need to continue with else statements, you can do the postfix form which developers coming from other languages also seem to quickly find appealing:

doSomething() unless $isUser && $isGuest;

Imagine the above without Perl's $sigils of course, but you can see how it allows an extra level of "positivity".

Basti Ortiz • Jul 14 '23

I must admit that I was initially skeptical (to say the least) when I saw the syntax, but that neat one-liner piqued my interest! Personally, that's gonna take some getting-used-to on my end, but I can definitely see why one would "instantly like" such a feature.

Dimitrios Kechagias • Jul 14 '23

And I am with you about early returns. I like to avoid them, except if that will cause a lot of indentation and general ugliness, but I don't think twice about adding them when it comes to this pattern:

return unless $isUser;

Feels natural. I don't use much javascript, but I see how it evolves nicely, so maybe something like that would not be a stretch to see added ;)

Eckehard • Jul 15 '23

Some JS programmers make extensive use of the ternary operator istead of conditionals to make their code "more compact". Carefully used, this can lead to readable code:

   // conditionals
   if (fruit === "apple")
       color = "green"
   else
       color = "red"

   // ternary operator
   color = (fruit === "apple") ? green : red

If you misuse the ternray operator as a short form of a conditional, this may make your code virtually unreadable:

something = condition ? nested_condition ? value_if_both_conditions_are_true
    : value_if_nested_condition_is_false : value_if_condition_is_false;

Here is a real life example:

let getPropDescriptor = proto => proto ?
      Obj.getOwnPropertyDescriptor(proto, k) ?? getPropDescriptor(protoOf(proto)) :
      _undefined

Gabrielle Niamat • Jul 12 '23

Totally agree with using the affirmative style for writing conditionals - the logical flow makes much more sense and is very intuitive to follow. Curious to know your thoughts on using the ternary operator in Python or JavaScript?

Basti Ortiz • Jul 12 '23

I don't mind them at all as long as they don't go two levels deep and beyond. 😅

Of course, the affirmative style must still follow from that.

name = 'admin' if is_admin else 'user'

const name = isAdmin ? 'admin' : 'user';

Anthony Fung • Jul 12 '23

I think ternary statements are useful for assigning const values where there is some conditional logic to it, like in your example above. I personally find it even easier to read if the two values are put on different lines (but I realise this will be subjective to styling preferences).

const name = isAdmin
  ? 'admin'
  : 'user';

There's only one reason I'll used nested ternaries: when writing variables in a dynamic HTML template and a return value must be computed in a single statement. Of course the workaround there is to compute it above the template where possible and then use it later.

DyllanUsher • Jul 18 '23

I feel like the example with

Not disallowed throw err
Else success path

Is a common way to structure your code to validate and clean up the success path conditions. Context is important though, I think overall it's more important to discuss the pattern with your team and try to come up with some pattern with justification. Having to negate things is not necessarily a good idea sometimes, but could make sense given the limitations of language, other context around the requirements, or existing patterns in the system.