128 lines
2.5 KiB
Markdown
128 lines
2.5 KiB
Markdown
# @babel/plugin-transform-classes
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> Compile ES2015 classes to ES5
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## Caveats
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When extending a native class (e.g., `class extends Array {}`), the super class
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needs to be wrapped. This is needed to workaround two problems:
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- Babel transpiles classes using `SuperClass.apply(/* ... */)`, but native
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classes aren't callable and thus throw in this case.
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- Some built-in functions (like `Array`) always return a new object. Instead of
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returning it, Babel should treat it as the new `this`.
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The wrapper works on IE11 and every other browser with `Object.setPrototypeOf` or `__proto__` as fallback.
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There is **NO IE <= 10 support**. If you need IE <= 10 it's recommended that you don't extend natives.
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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/plugin-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/plugin-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/plugin-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/plugin-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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