Readable over clever

A condensed one-liner feels great to write. It feels a lot less great to read six months later, during an incident, when you’re not the person who wrote it.

An example

Here’s a perfectly valid way to count active users per region:

const counts = users.reduce<Record<string, number>>(
	(acc, u) =>
		u.active ? { ...acc, [u.region]: (acc[u.region] ?? 0) + 1 } : acc,
	{},
);

And here’s one that someone skimming the file can follow top to bottom:

const counts: Record<string, number> = {};

for (const user of users) {
	if (!user.active) {
		continue;
	}
	counts[user.region] = (counts[user.region] ?? 0) + 1;
}

The second version is longer, but every line does one thing. It’s easier to step through in a debugger, too.

A useful test

Ask yourself: could someone unfamiliar with this code say what it does without reconstructing it in their head first? If not, it’s worth another pass.