class-field-definition.js

import { UUIDGen } from './utils/UUID.js';
const uuidGen = UUIDGen();

// Object property definition method
class User {
	constructor() {
		Object.define(this, 'uuid', {
			value: uuidGen.next(),
			writable: false,
			configurable: false
		});
	}
}

// Private field
class User {
	#uuid = uuidGen.next();
	get uuid() {
		return this.#uuid;
	}
}

// Definition shorthand
class User {
	uuid := {
		value: uuidGen.next(),
		writable: false,
		configurable: false
	}
}

definition-operator.js

const object = {
	a: 5
};

// Object property definition method
Object.defineProperty(object, 'aa', {
    get: () => object.a * 2,
	set: (value) => object.a = value / 2,
    enumerable: false
});

// Definition shorthand
object.aa := {
	get: () => object.a * 2,
	set: (value) => object.a = value / 2,
	enumerable: false
};