Javascript 设计模式

class SingleObject {
    login() {
        console.log('login...')
    }
}

SingleObject.getInstance = (function() {
    let instance
    return function() {
        if(!instance) {
            instance = new SingleObject()
        }
        return instance
    }
})()

class ReadImg {
    constructor(fileName) {
        this.fileName = fileName
        this.loadFromDisk()
    }
    
    display() {
        console.log('display...' + this.fileName)
    }
    
    loadFromDisk() {
        console.log('loading...' + this.fileName)
    }
}

class ProxyImg {
    constructor(fileName) {
        this.realImg = new ReadImg(fileName)
    }
    
    display() {
        this.realImg.display()
    }
}