unicorn/new-for-builtins

Some built-ins work with and without new, some throw without it, and some do something else. Array(3) is the same as new Array(3), Map() throws a TypeError, and Date() returns a string, not a Date. This rule requires new for built-in classes such as Array, Object, Date, Error, RegExp, Promise, Map, Set and the typed arrays.

The primitive wrappers are the other way around. new Boolean(false) is an object, so it's truthy, and typeof new String("a") is "object". new Symbol() and new BigInt(1) throw. Call these without new.

Configure#

Off by default. To turn it on:

[lint.rules]
"unicorn/new-for-builtins" = "error" # or "warn"

Examples#

const slots = Array(3);
const seen = Map();
const failure = Error("Not found");
const now = Date();

const enabled = new Boolean(false);
const total = new Number(input.value);

const slots = new Array(3);
const seen = new Map();
const failure = new Error("Not found");
const now = String(new Date());

const enabled = Boolean(input.checked);
const total = Number(input.value);

Object(value) === value is a common test for "is this an object", so it's allowed:

const isObject = value => Object(value) === value;

A name that your file declares or imports isn't the built-in, so it isn't checked:

import { Map } from "immutable";

const seen = Map();