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