unicorn/prefer-set-has

includes() walks the array from the start on every call. has() on a Set is a hash lookup, so it stays fast no matter how long the list gets.

The rule reports a const or let when all of this is true:

• Its value is a new array: an array literal, Array.from(), or the result of a method such as map() or filter().
• You only ever call .includes(value) on it.
• The lookup can run more than once, because there are two or more calls or the only call is inside a loop or a function.
• It isn't exported.

--fix wraps the array in new Set() and renames the calls to .has().

Configure

Off by default. To turn it on:

[lint.rules]
"unicorn/prefer-set-has" = "error" # or "warn"

Examples

Reported:

const blocked = ["admin", "root", "system"];

function isAllowed(name) {
  return !blocked.includes(name);
}

Not reported:

const blocked = new Set(["admin", "root", "system"]);

function isAllowed(name) {
  return !blocked.has(name);
}

An array that you search once, or that you also use as an array somewhere, can stay an array:

const formats = ["png", "jpeg"];
const isImage = formats.includes(extension);

const sizes = [16, 32, 64];
for (const icon of icons) {
  if (sizes.includes(icon.size)) draw(icon);
}
console.log(sizes.length);