builtinConstructorNews

Enforces using new for constructors that require it, and disallows new for primitive coercion functions.

✅ This rule is included in the ts stylistic and stylisticStrict presets.

Many built-in JavaScript objects have tricky behaviors around the new keyword. Some only work as expected when called with new, while others cannot or should not be called with new. This rule enforces consistent and safe calling of built-in JavaScript constructors using or not using new.

Specifically, this rule enforces using new for following built-in constructors:

Arrays and array-likes: Array, ArrayBuffer, SharedArrayBuffer, BigInt64Array, BigUint64Array, Float16Array, Float32Array, Float64Array, Int8Array, Int16Array, Int32Array, Uint8Array, Uint16Array, Uint32Array, Uint8ClampedArray
Common objects: Date, Error, Function, Object, Promise, RegExp
Common data structures: Map, WeakMap, Set, WeakSet
Other objects: DataView, Proxy, WeakRef, FinalizationRegistry

This rule disallows using new for following built-in constructors:

Using new with primitive coercion functions creates object wrappers that can cause unexpected behavior in comparisons and type checks.

const 
const list: any[]
list = 
var Array: ArrayConstructor
(arrayLength?: number) => any[] (+2 overloads)
Array(10);

const 
const now: string
now = 
var Date: DateConstructor
() => string
Enables basic storage and retrieval of dates and times.
Date();

const 
const map: any
map = 
var Map: MapConstructor
Map([["key", "value"]]);Error ts(2348)  ― Value of type 'MapConstructor' is not callable. Did you mean to include 'new'?

const 
const str: String
str = new 
var String: StringConstructor
new (value?: any) => String
Allows manipulation and formatting of text strings and determination and location of substrings within strings.
String("hello");

const 
const num: Number
num = new 
var Number: NumberConstructor
new (value?: any) => Number
An object that represents a number of any kind. All JavaScript numbers are 64-bit floating-point numbers.
Number(42);

const 
const list: any[]
list = new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(10);

const 
const now: Date
now = new 
var Date: DateConstructor
new () => Date (+3 overloads)
Date();

const 
const map: Map<string, string>
map = new 
var Map: MapConstructor
new <string, string>(iterable?: Iterable<readonly [string, string]> | null | undefined) => Map<string, string> (+3 overloads)
Map([["key", "value"]]);

const 
const str: string
str = 
var String: StringConstructor
(value?: any) => string
Allows manipulation and formatting of text strings and determination and location of substrings within strings.
String(
const value: any
value);

const 
const num: number
num = 
var Number: NumberConstructor
(value?: any) => number
An object that represents a number of any kind. All JavaScript numbers are 64-bit floating-point numbers.
Number(
const value: any
value);

Options

This rule is not configurable.

When Not To Use It

If you intentionally use object wrappers for primitives (e.g., new String()) for specific purposes like adding properties to a string value, you may disable this rule. For example, if you intentionally manage JavaScript primitives in a legacy codebase that does not adhere to common modern conventions, this rule may be counterproductive for you.

Equivalents in Other Linters

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builtinConstructorNews

Examples

Options

When Not To Use It

Further Reading

Equivalents in Other Linters