第一条是否等价于第二条呢

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    <img src="" alt="" id="img">
    <script>
        /*
                                              实现一个图片的加载；设置第一张图片加载1s之后加载第二张图片，可参考如下效果图：     
                                              http://img1.sycdn.imooc.com/climg//5b16558d00011ed506000338.jpg
                                              http://img1.sycdn.imooc.com/climg//5b165603000146ca06000338.jpg
                                              http://img1.sycdn.imooc.com/climg//5b1656140001c89906000338.jpg
                                                 
                                             第一步：设置一个函数，把图片的url地址作为参数
                                             第二步：实例化promise对象
                                             第三步：建立图像对象；设置图片的地址；把图片节点插入到body中
                                                                                        第四步：图片加载完成后执行resolve 
                                                                                        */
        const urlImgPromise = (url) => {
            return new Promise((resolve, reject) => {
                const img = new Image();
                //当图片加载完成
                img.onload = () => {
                    setTimeout(() => {
                        document.body.appendChild(img);
                        resolve();
                    }, 1000);

                }
                img.onerror = () => {
                    reject(new Error(`Could not load image at${url}`));
                }

                img.src = url;
            });
        };
        // const imgDOM = document.getElementById('img');
        // var imgnew = document.createElement('img');
        // var imgtwo = document.createElement('img');
        // document.body.appendChild(imgnew);
        // document.body.appendChild(imgtwo);
        urlImgPromise('http://img1.sycdn.imooc.com/climg//5b16558d00011ed506000338.jpg').then(() => {
            // setTimeout(() => {
            //     imgDOM.src = img.src;
            // }, 1000)

            // return urlImgPromise('http://img1.sycdn.imooc.com/climg//5b165603000146ca06000338.jpg'); //等价于
            
            return new Promise((resolve, reject) => {
                resolve(urlImgPromise('http://img1.sycdn.imooc.com/climg//5b165603000146ca06000338.jpg'));
            })
        }).catch(err => {
            console.log(err);
        }).then(() => {
            return urlImgPromise('http://img1.sycdn.imooc.com/climg//5b1656140001c89906000338.jpg');
        }).catch(err => {
            console.log(err);
        })
    </script>
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