unicorn/prefer-array-find

.filter() tests every element and builds a new array. If you only take the first or the last match from it, the rest of that work is thrown away. .find() and .findLast() stop at the match and return it.

Configure

Off by default. To turn it on:

[lint.rules]
"unicorn/prefer-array-find" = "error" # or "warn"

Examples

Reported:

const admin = users.filter(user => user.isAdmin)[0];
const first = users.filter(user => user.isActive).shift();
const [owner] = users.filter(user => user.isOwner);
const newest = users.filter(user => user.isActive).at(-1);
const lastGuest = users.filter(user => user.isGuest).pop();

Not reported:

const admin = users.find(user => user.isAdmin);
const first = users.find(user => user.isActive);
const owner = users.find(user => user.isOwner);
const newest = users.findLast(user => user.isActive);
const lastGuest = users.findLast(user => user.isGuest);

A variable that holds the result of .filter() is reported too, if you only read its first element:

const admins = users.filter(user => user.isAdmin);
notify(admins[0]);

If you use the variable in any other way, it's fine:

const admins = users.filter(user => user.isAdmin);
notify(admins[0]);
console.log(admins.length);