Invoking a constructor must use parentheses

Docs > Code Analysis > Static Analysis Rules > Invoking a constructor must use parentheses

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Metadata

ID: javascript-best-practices/new-parens

Language: JavaScript

Severity: Notice

Category: Best Practices

Description

This rule enforces the consistent use of parentheses in new statements. In JavaScript, you can omit parentheses when the constructor has no arguments, but you should always use them for consistency.

Non-Compliant Code Examples

// Default (Always)
var a = new Date;
var a = new Date
var a = new (Date);
var a = new (Date)
var a = (new Date)

// This `()` is `CallExpression`'s. This is a call of the result of `new Date`.
var a = (new Date)()
var a = new foo.Bar;
var a = (new Foo).bar;

// Explicit always
var a = new Date;
var a = new foo.Bar;
var a = (new Foo).bar;
var a = new new Foo()

// OPTION never not supported
// Never
// var a = new Date();
// var a = new Date()
// var a = new (Date)();
// var a = new (Date)()
// var a = (new Date())
// var a = (new Date())()
// var a = new foo.Bar();
// var a = (new Foo()).bar;
// var a = new new Foo()

Compliant Code Examples

// Default (Always)
var a = new Date();
var a = new Date(function() {});
var a = new (Date)();
var a = new ((Date))();
var a = (new Date());
var a = new foo.Bar();
var a = (new Foo()).bar;

// Explicit Always
var a = new Date();
var a = new foo.Bar();
var a = (new Foo()).bar;

// OPTION never not supported
// Never
// var a = new Date;
// var a = new Date(function() {});
// var a = new (Date);
// var a = new ((Date));
// var a = (new Date);
// var a = new foo.Bar;
// var a = (new Foo).bar;
// var a = new Person('Name')
// var a = new Person('Name', 12)
// var a = new ((Person))('Name');