Is it in there?

array.includes(x) and string.includes(sub) answer yes or no; indexOf gives the position or -1.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

Allow-lists, feature flags, 'did the user pick this', search boxes: membership is a daily question.

How to think about it

Do I need yes/no, or the position? If you only need yes/no, includes reads best. If you need the position, indexOf. For many checks against a big list, build a Set first.

Worked example

const roles = ["admin", "editor"];

Two roles.

roles.includes("editor")

true.

roles.indexOf("viewer")

-1: not found.

"hello".includes("ell")

true: substrings too.

Your turn

Reject a name that is on the banned list.

if (banned.(name)) return false;

The trap

includes uses ===, so it finds NaN but never an object equal by contents. Two {a:1} objects are not the same object.

Practise is it in there on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.