/********    代理类实现每张图片的loading     ********/
  
    function Img() {
        this.img = document.createElement('img')
        document.body.appendChild(this.img)
    }
    Img.prototype.setSrc = function (src) {
        this.img.src = src
    }
    //代理函数
    function ProxyImg(src) {
        this.img = new Img()
        this.img.setSrc('./loading.png') //先设置loading图片

        let image = new Image();
        image.src = src;
        let self = this;
        //图片加载完毕后   ---->   再显示真正的图片
        image.onload = function () {
            self.img.setSrc(src)
        }
    }
    new ProxyImg('./1.png')
    new ProxyImg('./2.png')
    new ProxyImg('./3.png')
    new ProxyImg('./4.png')
    new ProxyImg('./5.png')