150 lines
2.7 KiB
Markdown
150 lines
2.7 KiB
Markdown
# @babel/plugin-proposal-class-properties
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> This plugin transforms class properties
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## Example
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Below is a class with four class properties which will be transformed.
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```js
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class Bork {
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//Property initializer syntax
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instanceProperty = "bork";
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boundFunction = () => {
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return this.instanceProperty;
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};
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//Static class properties
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static staticProperty = "babelIsCool";
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static staticFunction = function() {
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return Bork.staticProperty;
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};
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}
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let myBork = new Bork;
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//Property initializers are not on the prototype.
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console.log(myBork.__proto__.boundFunction); // > undefined
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//Bound functions are bound to the class instance.
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console.log(myBork.boundFunction.call(undefined)); // > "bork"
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//Static function exists on the class.
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console.log(Bork.staticFunction()); // > "babelIsCool"
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```
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## Installation
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```sh
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npm install --save-dev @babel/plugin-proposal-class-properties
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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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Without options:
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```json
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{
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"plugins": ["@babel/proposal-class-properties"]
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}
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```
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With options:
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```json
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{
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"plugins": [
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["@babel/proposal-class-properties", { "loose": true }]
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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/proposal-class-properties 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/proposal-class-properties"]
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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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When `true`, class properties are compiled to use an assignment expression instead of `Object.defineProperty`.
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#### Example
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```js
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class Bork {
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static a = 'foo';
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static b;
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x = 'bar';
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y;
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}
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```
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Without `{ "loose": true }`, the above code will compile to the following, using `Object.definePropery`:
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```js
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var Bork = function Bork() {
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babelHelpers.classCallCheck(this, Bork);
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Object.defineProperty(this, "x", {
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configurable: true,
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enumerable: true,
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writable: true,
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value: 'bar'
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});
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Object.defineProperty(this, "y", {
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configurable: true,
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enumerable: true,
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writable: true,
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value: void 0
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});
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};
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Object.defineProperty(Bork, "a", {
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configurable: true,
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enumerable: true,
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writable: true,
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value: 'foo'
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});
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Object.defineProperty(Bork, "b", {
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configurable: true,
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enumerable: true,
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writable: true,
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value: void 0
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});
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```
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However, with `{ "loose": true }`, it will compile using assignment expressions:
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```js
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var Bork = function Bork() {
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babelHelpers.classCallCheck(this, Bork);
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this.x = 'bar';
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this.y = void 0;
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};
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Bork.a = 'foo';
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Bork.b = void 0;
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```
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## References
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* [Proposal: ES Class Fields & Static Properties](https://github.com/jeffmo/es-class-static-properties-and-fields)
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