Promise.all():
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1 <body>
2 <div id="pic" ></div>
3 <script>
4 const imgs = [
5 'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1588606301799&di=26e46595e4a886700fb38dd008909934&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201710%2F07%2F20171007134945_84Cnd.jpeg',
6 'https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=1426668281,3085506529&fm=26&gp=0.jpg',
7 'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1588606301800&di=28eb474abf2022fb1f4f7e1525882fa3&imgtype=0&src=http%3A%2F%2Fgss0.baidu.com%2F7LsWdDW5_xN3otqbppnN2DJv%2Fzhidao%2Fpic%2Fitem%2Fdcc451da81cb39db719c5aa3db160924aa1830e2.jpg'
8 ];
9
10
11 function loadImagePro(picUrl) {
12 return new Promise(function (resolve, reject) {
13 const img = new Image();
14 img.src = picUrl;
15 img.onload = () => void resolve(img); // 将标签元素传入resolve
16 // img.onerror = reject('加载失败');
17 });
18 }
19 /*
20 // 返回一个Promise实例组成的数组
21 const promiseArr = imgs.map(picUrl => loadImagePro(picUrl));
22
23 Promise.all(promiseArr)
24 .then(function (picArr) {
25 console.log(picArr); // 返回所有标签元素组成的数组
26 picArr.forEach(function (item) {
27 console.log(item);
28 document.getElementById('pic').appendChild(item);
29 });
30 });
31 */
32
33 // ES6 写法
34 Promise.all(imgs.map(picUrl => loadImagePro(picUrl)))
35 .then(picArr => {
36 picArr.forEach(item => document.getElementById('pic').appendChild(item));
37 });
38 console.log('末尾');
39 </script>
40 </body>
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Promise.race():
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1 <body>
2 <div id="pic" ></div>
3 <script>
4 const imgs = [
5 'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1588606301799&di=26e46595e4a886700fb38dd008909934&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201710%2F07%2F20171007134945_84Cnd.jpeg',
6 'https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=1426668281,3085506529&fm=26&gp=0.jpg',
7 'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1588606301800&di=28eb474abf2022fb1f4f7e1525882fa3&imgtype=0&src=http%3A%2F%2Fgss0.baidu.com%2F7LsWdDW5_xN3otqbppnN2DJv%2Fzhidao%2Fpic%2Fitem%2Fdcc451da81cb39db719c5aa3db160924aa1830e2.jpg'
8 ];
9
10
11 function loadImagePro(picUrl) {
12 return new Promise(function (resolve, reject) {
13 const img = new Image();
14 img.src = picUrl;
15 img.onload = () => void resolve(img); // 将标签元素传入resolve
16 // img.onerror = reject('加载失败');
17 });
18 }
19
20 // 返回一个Promise实例组成的数组
21 const promiseArr = imgs.map(picUrl => loadImagePro(picUrl));
22
23 // 只接收promiseArr数组中，最先返回的promise实列，然后执行这个实例的.then()
24 // Promise.race(promiseArr).then(function (item) {// 接收到Promise.race返回的标签元素
25 // document.getElementById('pic').appendChild(item);
26 // });
27
28 // ES6 写法
29 Promise.race(imgs.map(picUrl => loadImagePro(picUrl))).then(item => document.getElementById('pic').appendChild(item));
30
31 console.log('末尾');
32 </script>
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