unicorn/prefer-array-index-of

.findIndex() is for a test that === can't express. If the callback only compares the element with a value, .indexOf(value) does the same thing without a function. The same goes for .findLastIndex() and .lastIndexOf().

Configure

Off by default. To turn it on:

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

Examples

Reported:

const index = names.findIndex(name => name === "admin");
const last = names.findLastIndex(name => name === current);

Not reported:

const index = names.indexOf("admin");
const last = names.lastIndexOf(current);

A callback that compares a property of the element, or compares with ==, isn't reported:

const index = users.findIndex(user => user.name === "admin");
const loose = ids.findIndex(id => id == "7");