js的几种设计模式

const Singleton = (function () {
    let instance;
    function createInstance() {
        const object = new Object("I am the instance");
        return object;
    }
    return {
        getInstance: function () {
            if (!instance) {
                instance = createInstance();
            }
            return instance;
        }
    };
})();

function Car(make, model, year) {
    this.make = make;
    this.model = model;
    this.year = year;
}

function Truck(make, model, year) {
    this.make = make;
    this.model = model;
    this.year = year;
}

function VehicleFactory() {}

VehicleFactory.prototype.vehicleClass = Car;

VehicleFactory.prototype.createVehicle = function (make, model, year) {
    if (this.vehicleClass) {
        return new this.vehicleClass(make, model, year);
    } else {
        throw new Error('Invalid vehicle class');
    }
};

class Subject {
    constructor() {
        this.observers = [];
    }

    addObserver(observer) {
        this.observers.push(observer);
    }

    removeObserver(observer) {
        const index = this.observers.indexOf(observer);
        if (index!== -1) {
            this.observers.splice(index, 1);
        }
    }

    notify(data) {
        this.observers.forEach(observer => observer.update(data));
    }
}

class Observer {
    update(data) {
        console.log('Received data:', data);
    }
}

const Module = (function () {
    let privateVar = 'I am private';

    function privateMethod() {
        console.log(privateVar);
    }

    return {
        publicMethod: function () {
            privateMethod();
        }
    };
})();

class Image {
    constructor(url) {
        this.url = url;
        this.loadImage();
    }

    loadImage() {
        console.log(`Loading image from ${this.url}`);
    }
}

class ImageProxy {
    constructor(url) {
        this.url = url;
        this.image = null;
    }

    showImage() {
        if (!this.image) {
            this.image = new Image(this.url);
        }
        this.image.loadImage();
    }
}