@babel/plugin-proposal-class-properties
Example
Below is a class with four class properties which will be transformed.
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
npm install --save-dev @babel/plugin-proposal-class-properties
Usage
With a configuration file (Recommended)
Without options:
{
"plugins": ["@babel/plugin-proposal-class-properties"]
}
With options:
{
"plugins": [
["@babel/plugin-proposal-class-properties", { "loose": true }]
]
}
Via CLI
babel --plugins @babel/plugin-proposal-class-properties script.js
Via Node API
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.
For an explanation of the consequences of using either, see Definition vs. Assignment (TL;DR in Part 5)
Example
class Bork {
static a = 'foo';
static b;
x = 'bar';
y;
}
Without { "loose": true }, the above code will compile to the following, using Object.defineProperty:
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:
var Bork = function Bork() {
babelHelpers.classCallCheck(this, Bork);
this.x = 'bar';
this.y = void 0;
};
Bork.a = 'foo';
Bork.b = void 0;
You can read more about configuring plugin options here