628061c501
* Add new.target transform * Catch new.target under only an arrow function * More unsupported reflect.construct cases * Fix node 4 test * Do not transform Methods * More tests * Properly setup function inheritance test * Tests tests tests * Fix ES6 class's new.target * Remove expected output thats supposed to throw.
105 lines
1.8 KiB
Markdown
105 lines
1.8 KiB
Markdown
# babel-plugin-transform-new-target
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This plugins allows babel to transform `new.target` meta property into a
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(correct in most cases) `this.constructor` expression.
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## Example
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```js
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function Foo() {
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console.log(new.target);
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}
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Foo(); // => undefined
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new Foo(); // => Foo
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```
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```js
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class Foo {
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constructor() {
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console.log(new.target);
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}
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}
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class Bar extends Foo {
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}
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new Foo(); // => Foo
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new Bar(); // => Bar
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```
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### Caveats
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This plugin relies on `this.constructor`, which means `super` must
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already have been called when using untransformed classes.
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```js
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class Foo {}
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class Bar extends Foo {
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constructor() {
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// This will be a problem if classes aren't transformed to ES5
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new.target;
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super();
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}
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}
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```
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Additionally, this plugin cannot transform all `Reflect.construct` cases
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when using `newTarget` with ES5 function classes (transformed ES6 classes).
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```js
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function Foo() {
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console.log(new.target);
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}
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// Bar extends Foo in ES5
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function Bar() {
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Foo.call(this);
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}
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Bar.prototype = Object.create(Foo.prototype);
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Bar.prototype.constructor = Bar;
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// Baz does not extend Foo
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function Baz() {}
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Reflect.construct(Foo, []); // => Foo (correct)
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Reflect.construct(Foo, [], Bar); // => Bar (correct)
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Reflect.construct(Bar, []); // => Bar (incorrect, though this is how ES5
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// inheritience is commonly implemented.)
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Reflect.construct(Foo, [], Baz); // => undefined (incorrect)
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```
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## Installation
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```sh
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npm install --save-dev babel-plugin-transform-new-target
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```
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## Usage
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### Via `.babelrc` (Recommended)
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**.babelrc**
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```json
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{
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"plugins": ["transform-new-target"]
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}
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```
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### Via CLI
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```sh
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babel --plugins transform-new-target script.js
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```
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### Via Node API
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```javascript
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require("babel-core").transform("code", {
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plugins: ["transform-new-target"]
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});
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```
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