unicorn/no-array-callback-reference

map, filter, and the other array methods call their callback with three arguments: the element, its index, and the array. A function that you pass by name receives all three. If it has an optional second parameter, or gets one in a later version of its library, the index ends up there.

The rule checks every, filter, find, findLast, findIndex, findLastIndex, flatMap, forEach, map, some, reduce, and reduceRight.

Configure

Off by default. To turn it on:

[lint.rules]
"unicorn/no-array-callback-reference" = "error" # or "warn"

Examples

Reported:

const sizes = ["10", "10", "10"].map(parseInt); // [10, NaN, 2]

import { formatUser } from "./format.js";

const lines = users.map(formatUser);

Not reported:

const sizes = ["10", "10", "10"].map((text) => parseInt(text, 10)); // [10, 10, 10]

import { formatUser } from "./format.js";

const lines = users.map((user) => formatUser(user));

Built-in constructors such as Boolean, String, and Number are allowed, and so is a function made with .bind():

const present = values.filter(Boolean);
const labels = ids.map(String);
const rows = items.map(table.render.bind(table));

The rule can't tell what's an array. It skips calls on a property, such as store.users.map(), and on common library names, such as _, lodash, $, jQuery, React, and Vue:

const lines = store.users.map(formatUser);
const names = _.map(users, formatUser);