How to use the ternary statement sensibly in JavaScript

How to use the ternary statement sensibly in JavaScript cover image

The way we choose to write our code is as important as what the code does, poorly structured, poorly name or plain old confusing code is hard to maintain. While the problems we solve are often mind bendingly difficult, the way we write our code does not have to be.

We have all opened up code that looks like this:

const fds = (fda + fdb)/gtr;

and wondered if the original author hated the universe, was a genuine genius or was somehow allergic to typing. There is nothing in that code to indicate what those variable relate to or how fds might be useful in the future.

The variable names are meaningless to our brain and remembering these letter groupings while tracing their use through the code adds a huge amount of cognitive load.

Fortunately we have, in the main, moved away from this type of variable naming. It was ripe in the Fortran and early C days but now we use more descriptive names that show the intent of the code and it is much easier follow along. If a variable is called maxWidth it is much easier to understand and remember than mW. It's the different between holding a group of letters in your head vs the concept of what it represents, are brains are pretty terrible at the former but excellent at the latter.

Ternaries and Destructuring

Whilst we have clearly improved when it comes to naming variables there is an area of coding that we are going backwards in, and that is the desire for smaller and smaller files - even at the cost of legibility.

Small composable blocks of code is a great ideal to aim for, having 45 tabs open in a code editor isn't always ideal but it probably is better than 3 files of 2,000+ lines each. However, I would rather have those 3 big files to wrangle than dozens or hundreds of the following:

const {
  data: {
    header: { personId, storeId, locationId, stockUnit },
  },
} = msg;

or

const result = isAdmin ? "All Allowed" : isManager ? "Some Allowed" : isAlien ? "Run" : "Not Allowed";

In isolation the above examples are reasonably understandable (i've chosen fairly simple examples) however, amongst a full application, surrounded by other business logic and less straightforward variable names, both of these can be written in a longer, more understandable manner. Let's take that ternary:

let result = "Not Allowed";
if (isAdmin) {
  result = "All Allowed";
}
if (isManager) {
  result = "Some Allowed";
}
if (isAlien) {
  result = "Run";
}

The above is considerably longer but much easier to read. The added vertical space is a more than worthwhile tradeoff in the aid of readability to me.

We should be striving to write code that is understandable to the newest and least experienced members of the team. Business logic is where the complexity should lie in code, not in the syntax itself. When a new developer or new team member is reading unfamiliar code they should be focussing all of their efforts on understanding the what the code does and not the exotic structures used to save a few lines.

The rise of ternary

Ternary operators have always been a bit of syntactic sugar to make very simple if/else statements shorter. I would agree that an if/else that takes up only 5 lines and is very simple should be simplified, however the rise in ternary in the Javascript world over the last decade is starting to get out of hand. I'm starting to see multi level ternaries with map and find in them where that all important : of the ternary becomes impossible to spot.

I think this has happened thanks to React, more specifically JSX, and it's liberal use of ternary statements for conditional rendering. I don't want this to become a rant on JSX (which at worst I would say I am ambivalent on) but let's not let JSX practices bleed in to JS/TS and other best practice.

Take Away

Code for legibility and not brevity. We moved away from terse and incomprehensible variable names, let's not regress with the equivalent with syntax.

If you want a selfish motivation then I ask: would you rather new team members just understand the code you wrote or spend the rest of your days in that company answering questions about it?

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