122 lines
2.3 KiB
Markdown
122 lines
2.3 KiB
Markdown
# @babel/plugin-transform-classes
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> Compile ES2015 classes to ES5
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## Caveats
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Built-in classes such as `Date`, `Array`, `DOM` etc cannot be properly subclassed
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due to limitations in ES5 (for the [classes](http://babeljs.io/docs/plugins/transform-classes) plugin).
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You can try to use [babel-plugin-transform-builtin-extend](https://github.com/loganfsmyth/babel-plugin-transform-builtin-extend) based on `Object.setPrototypeOf` and `Reflect.construct`, but it also has some limitations.
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## Examples
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**In**
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```javascript
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class Test {
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constructor(name) {
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this.name = name;
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}
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logger () {
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console.log("Hello", this.name);
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}
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}
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```
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**Out**
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```javascript
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function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
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var Test = function () {
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function Test(name) {
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_classCallCheck(this, Test);
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this.name = name;
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}
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Test.prototype.logger = function logger() {
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console.log("Hello", this.name);
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};
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return Test;
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}();
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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-classes
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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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```js
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// without options
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{
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"plugins": ["@babel/transform-classes"]
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}
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// with options
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{
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"plugins": [
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["@babel/transform-classes", {
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"loose": true
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}]
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]
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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 @babel/transform-classes 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: ["@babel/transform-classes"]
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});
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```
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## Options
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### `loose`
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`boolean`, defaults to `false`.
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#### Method enumerability
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Please note that in loose mode class methods **are** enumerable. This is not in line
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with the spec and you may run into issues.
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#### Method assignment
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Under loose mode, methods are defined on the class prototype with simple assignments
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instead of being defined. This can result in the following not working:
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```javascript
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class Foo {
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set bar() {
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throw new Error("foo!");
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}
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}
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class Bar extends Foo {
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bar() {
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// will throw an error when this method is defined
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}
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}
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```
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When `Bar.prototype.foo` is defined it triggers the setter on `Foo`. This is a
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case that is very unlikely to appear in production code however it's something
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to keep in mind.
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