本實例的實現(xiàn)原理比較簡單，不過不是真正的按文件大小來顯示加載進度的，只是在觸發(fā)document.onreadystatechange事件時，根據(jù)document.readyState的狀態(tài)來改變顯示進度的。其實還有一種靠譜一點的方法，用XMLHttpRequest對象的實例的progress事件，詳細解讀XMLHttpRequest，如：

 var request = new XMLHttpRequest();
 request.onprogress = function (e) {
 if(e.lengthComputable){ //lengthComputable是指文件是否有大小，值為true、false
 progress.innerHTML = Math.round(100* e.loaded/ e.total) + \'%\'; //loaded、total表示已經(jīng)加載的大小和總大小
 }
 }

用以上方法實現(xiàn)起來也挺麻煩，而且也不能實現(xiàn)100%的真實加載進度，所以我索性就假一點了，不用他了！

本實例還用到了document.styleSheets[0].insertRule()方法，這里有我對它的總結(jié)：用原生JS讀寫CSS樣式的方法總結(jié)

關(guān)于CSS動畫的實現(xiàn)，大家自己看代碼吧，很簡單的代碼，如果看的吃力，建議去補補CSS基礎(chǔ)了，介紹個干貨，CSS中文參考手冊網(wǎng)站，我表達能力有限，就不在這里嚼口舌了

下面是完整代碼+演示：

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>蘇福的作品</title>
 <script>
 document.onreadystatechange = function () {
 function $id(id){return document.getElementById(id)}
 var width = 0,id,
 preloader_line = $id('preloader_line').firstElementChild,
 preloader = $id('preloader'),
 preloader_center = $id('preloader_center'),
 preloader_btn = $id('preloader_btn'),
 preloader_loading = $id('preloader_loading');
 if (document.readyState == "interactive") {
 loading(1,110,50);
 }
 if (document.readyState == "complete") {
 loading(5,120,16.7);
 preloader_loading.id = 'preloader_loaded';
 preloader_loading.innerHTML = 'Loading Complete'+'<br/>'+'Using: '+performance.now().toFixed(3)+' ms';
 preloader_btn.innerHTML = 'E N T E R';
 preloader_btn.style.borderBottom = '4px solid green';
 preloader_btn.style.fontStyle = 'inherit';
 preloader_btn.style.fontSize = '24px';
 if(document.styleSheets[0].insertRule){
 document.styleSheets[0].insertRule('#preloader_btn:hover{border-bottom: 4px solid green;border-radius: 60px;color: red;}',0);
 }else{//兼容IE9以下
 document.styleSheets[0].addRule('#preloader_btn:hover{border-bottom: 4px solid green;border-radius: 60px;color: red;}',0);
 }
 preloader_btn.onclick = function () {
 var opacity = 1,id;
 function hide(){
 if(opacity<=0){
 clearTimeout(id);
 preloader.style.display = 'none';
 document.body.style.overflow = 'auto';
 return;
 }
 opacity -= 0.1;
 preloader.style.opacity = opacity;
 id = setTimeout(function(){
 hide();
 },50);
 }
 hide();
 };
 }
 function loading(step,max,time){
 if(width>=max){
 clearTimeout(id);
 if(max >= 120){
 preloader_line.parentNode.style.display = 'none';
 }
 return;
 }
 width += step;
 preloader_line.style.width = width+'px';
 id = setTimeout(function(){
 loading(step,max,time);
 },time);
 }
 };
 </script>
 <style>
 body{
 overflow: hidden;
 }
 #preloader{
 position: absolute;
 width: 100%;
 height: 100%;
 background-color: white;
 z-index: 999;
 }
 #preloader_center{
 position: absolute;
 left: 0;
 right: 0;
 top: 0;
 bottom: 0;
 width: 150px;
 height: 75px;
 margin:auto;
 }
 #preloader_loading{
 position: absolute;
 left: 0;
 right: 0;
 top: 45px;
 margin: auto;
 width: 96px;
 height: 30px;
 }
 #preloader_loaded{
 position: absolute;
 left: 0;
 right: 0;
 top: 45px;
 margin: auto;
 font-size: 12px;
 text-align: center;
 line-height: 30px;
 }
 #preloader_loading span{
 position: absolute;
 width: 10px;
 height: 2px;
 top: 0;
 bottom: 0;
 margin:auto;
 background-color: #9b59b6;
 animation: loading 1.5s infinite ease-in-out ;
 }
 #preloader_loading span:nth-child(2){
 left: 12px;
 animation-delay: .1s;
 }
 #preloader_loading span:nth-child(3){
 left: 24px;
 animation-delay: .2s;
 }
 #preloader_loading span:nth-child(4){
 left: 36px;
 animation-delay: .3s;
 }
 #preloader_loading span:nth-child(5){
 left: 48px;
 animation-delay: .4s;
 }
 #preloader_loading span:nth-child(6){
 left: 50px;
 animation-delay: .5s;
 }
 #preloader_loading span:nth-child(7){
 left: 62px;
 animation-delay: .6s;
 }
 #preloader_loading span:nth-child(8){
 left: 74px;
 animation-delay: .7s;
 }
 #preloader_loading span:nth-child(9){
 left: 86px;
 animation-delay: .8s;
 }
 @keyframes loading {
 0%{height: 2px;background:#9b59b6;}
 15%{height: 20px;background:#3498db;}
 50%{height: 2px;background:#9b59b6;}
 100%{height: 2px;background:#9b59b6;}
 }
 iframe{width: 100%;height: 1000px;}
 #preloader_btn{
 position: absolute;
 left: 0;
 right: 0;
 top: 0;
 margin:auto;
 display: block;
 width: 122px;
 height: 40px;
 font-size: 14px;
 text-align: center;
 line-height: 40px;
 cursor: pointer;
 color: #9b59b6;
 font-style: italic;
 -webkit-transition: all .5s;
 -moz-transition: all .5s;
 -ms-transition: all .5s;
 -o-transition: all .5s;
 transition: all .5s;
 }
 #preloader_line{
 position: absolute;
 left: 0;
 right: 0;
 top: 40px;
 margin:auto;
 width: 120px;
 height: 2px;
 border: 1px solid green;
 }
 #preloader_line span{
 display: block;
 height: 2px;
 width: 0;
 background-color: green;
 }
 </style>
</head>
<body>
<div id="preloader">
 <div id="preloader_center">
 <span id="preloader_btn">Loading...</span>
 <span id="preloader_line">
 <span></span>
 </span>
 <div id="preloader_loading">
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 </div>
 </div>
</div>
<iframe src="http://jd.com"></iframe>
</body>
</html>

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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