diff options
Diffstat (limited to 'node_modules/@babel/plugin-transform-new-target/README.md')
| -rw-r--r-- | node_modules/@babel/plugin-transform-new-target/README.md | 104 |
1 files changed, 104 insertions, 0 deletions
diff --git a/node_modules/@babel/plugin-transform-new-target/README.md b/node_modules/@babel/plugin-transform-new-target/README.md new file mode 100644 index 00000000..ccd5b4a4 --- /dev/null +++ b/node_modules/@babel/plugin-transform-new-target/README.md @@ -0,0 +1,104 @@ +# @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"] +}); +``` |
