The new.target
property lets you detect whether a function or constructor was called using the new operator. In constructors and functions instantiated with the new operator, new.target
returns a reference to the constructor or function. In normal function calls, new.target
is undefined
.
Syntax
new.target
Description
The new.target
syntax consists of the keyword "new
", a dot, and a property name "target"
. Normally "new."
serves as the context for a property access, but here "new."
is not really an object. In constructor calls, however, new.target
refers the constructor invoked by new
and so "new.
" becomes a virtual context.
The new.target
property is a meta property that is available to all functions. In arrow functions, new.target
refers to the new.target
of the surrounding function.
Examples
new.target in function calls
In normal function calls (as opposed to constructor function calls), new.target
is undefined
. This lets you detect if a function was called with new as a constructor.
function Foo() { if (!new.target) throw "Foo() must be called with new"; console.log("Foo instantiated with new"); } Foo(); // throws "Foo() must be called with new" new Foo(); // logs "Foo instantiated with new"
new.target in constructors
In class constructors, new.target
refers to the constructor that was directly invoked by new
. This is also the case if the constructor is in a parent class and was delegated from a child constructor.
class A { constructor() { console.log(new.target.name); } } class B extends A { constructor() { super(); } } var a = new A(); // logs "A" var b = new B(); // logs "B"
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Built-in Function Objects' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Built-in Function Objects' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 46.0 | 41 (41) | No support | No support | No support |
Feature | Android | Android Webview | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|
Basic support | No support | 46.0 | 41.0 (41) | No support | No support | No support | 46.0 |