@babel/plugin-transform-new-target
NOTE: This plugin is included in
@babel/preset-env
Example
function Foo() { console.log(new.target); } Foo(); // => undefined new Foo(); // => Foo
class Foo { constructor() { console.log(new.target); } } class Bar extends Foo {} new Foo(); // => Foo new Bar(); // => Bar
Caveats
This plugin relies on this.constructor
, which means super
must already have been called when using untransformed classes.
class Foo {} class Bar extends Foo { constructor() { // This will be a problem if classes aren't transformed to ES5 new.target; super(); } }
Additionally, this plugin cannot transform all Reflect.construct
cases when using newTarget
with ES5 function classes (transformed ES6 classes).
function Foo() { console.log(new.target); } // Bar extends Foo in ES5 function Bar() { Foo.call(this); } Bar.prototype = Object.create(Foo.prototype); Bar.prototype.constructor = Bar; // Baz does not extend Foo function Baz() {} Reflect.construct(Foo, []); // => Foo (correct) Reflect.construct(Foo, [], Bar); // => Bar (correct) Reflect.construct(Bar, []); // => Bar (incorrect, though this is how ES5 // inheritance is commonly implemented.) Reflect.construct(Foo, [], Baz); // => undefined (incorrect)
Installation
npm install --save-dev @babel/plugin-transform-new-target
Usage
With a configuration file (Recommended)
{ "plugins": ["@babel/plugin-transform-new-target"] }
Via CLI
babel --plugins @babel/plugin-transform-new-target script.js
Via Node API
require("@babel/core").transformSync("code", { plugins: ["@babel/plugin-transform-new-target"], });