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# @babel/plugin-transform-new-target
This plugins allows babel to transform `new.target` meta property into a
(correct in most cases) `this.constructor` expression.
## Example
```js
function Foo() {
console.log(new.target);
}
Foo(); // => undefined
new Foo(); // => Foo
```
```js
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.
```js
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).
```js
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
// inheritience is commonly implemented.)
Reflect.construct(Foo, [], Baz); // => undefined (incorrect)
```
## Installation
```sh
npm install --save-dev @babel/plugin-transform-new-target
```
## Usage
### Via `.babelrc` (Recommended)
**.babelrc**
```json
{
"plugins": ["@babel/plugin-transform-new-target"]
}
```
### Via CLI
```sh
babel --plugins @babel/plugin-transform-new-target script.js
```
### Via Node API
```javascript
require("@babel/core").transform("code", {
plugins: ["@babel/plugin-transform-new-target"]
});
```
|
