图片预加载之有序预加载

Posted 2020-09-17

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<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>PreLoading</title>
    <style>
        *{margin:0; padding:0; border:none; outline:0; text-decoration:none;}
        html,body,.box{width:100%; height:100%;}
        .box{display:none;}
        #img{width:90%; height:90%; margin:2vh auto 0; display:block; box-shadow:0 0 10px gray;}
        .box .btns{width:140px; height:40px; display:block; margin:20px auto;}
        .box .btns .btn{width:60px; height:40px; display:block; border:1px gray solid; background-color:#ccc; text-align:center; line-height:40px; float:left;}
        .box .btns .btn:nth-of-type(2){margin-left:16px;}

        .load{width:100%; height:100%; display:block; font-size:60px; font-family:"微软雅黑"; color:#ccc; text-align:center; line-height:100vh; position:fixed;}
    </style>
</head>
<body>
    <div class="box">
        <img id="img" src="" alt="pic">
        <p class="btns"><a href="javascript:" class="btn">prev</a><a href="javascript:" class="btn">next</a></p>
    </div>
    <p class="load">0%</p>

    <script type="text/javascript">

        var imgs = [‘http://down.699pic.com/photo/50036/7661.jpg?_upt=da51378d1494571758&_upd=500367661.jpg‘,
                    ‘http://desk.fd.zol-img.com.cn/t_s1920x1080c5/g5/M00/09/0F/ChMkJljskIqIPX9bAAMPyuIn8DcAAbj8QB7XpYAAw_i343.jpg‘,
                    ‘http://desk.fd.zol-img.com.cn/t_s1920x1080c5/g5/M00/09/0F/ChMkJljskLeIaW-JAAIudN_yqvgAAbj8gDQO5AAAi6M64.jpeg‘,
                    ‘http://desk.fd.zol-img.com.cn/t_s1920x1080c5/g5/M00/0F/08/ChMkJlauzISIH0uXAARUHuJLVX8AAH8-gHu6zsABFQ2166.jpg‘,
                    ‘http://desk.fd.zol-img.com.cn/t_s1920x1080c5/g5/M00/0F/08/ChMkJlauzISIIL5TAAObxg4-XeUAAH8-gHzP3EAA5ve000.jpg‘];
        
        // 绑定按钮事件

        var btns = document.getElementsByClassName(‘btn‘),
            img = document.getElementById(‘img‘),
            index = 0;

        for(var i=0;i<btns.length;i++){
            btns[i].onclick = function(){
                if(this.innerHTML === ‘next‘){
                    index = Math.min(++index , imgs.length-1);
                    img.setAttribute(‘src‘,imgs[index]);
                }
                if(this.innerHTML === ‘prev‘){
                    index = Math.max(--index , 0);
                    img.setAttribute(‘src‘,imgs[index]);
                }
            }
        }

        // 计数变量

        var count = 0,
            load = document.getElementsByClassName(‘load‘)[0],
            box = document.getElementsByClassName(‘box‘)[0];

        // 有序预加载

        var imgObj = new Image();        
        function loading(){
            imgObj.onload = function(){
                load.innerHTML = Math.round((count + 1) / imgs.length * 100) + ‘%‘;
                if(count >= imgs.length){
                    load.style.display = ‘none‘;
                    box.style.display = ‘block‘;
                    img.setAttribute(‘src‘,imgs[0]);
                    document.title = ‘1/‘ + imgs.length;
                }
                else{
                    loading();
                }
            }
            imgObj.onerror = function(){
                load.innerHTML = Math.round((count + 1) / imgs.length * 100) + ‘%‘;
                if(count >= imgs.length){
                    load.style.display = ‘none‘;
                    box.style.display = ‘block‘;
                    img.setAttribute(‘src‘,imgs[0]);
                    document.title = ‘1/‘ + imgs.length;
                }
                else{
                    loading();
                }
            }
            imgObj.src = imgs[count];
            count++;
        }
        loading();
    </script>
</body>
</html>

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