因为像img等替换元素是没有伪类的::before, ::after, 可以用其特征实现，图片未加载时信息的显示效果
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>替换元素的妙用1</title>
<style type="text/css">
img {
display: inline-block;
width: 200px;
height: 200px;
/* 隐藏Firefox alt文字 */
color: transparent;
position: relative;
overflow: hidden;
}
img:not([src]) {
/* 隐藏Chrome alt文字以及银色边框 */
visibility: hidden;
}
img::before {
/* 淡蓝色占位背景 */
content: "";
position: absolute; left: 0;
width: 100%; height: 100%;
background-color: #f0f3f9;
visibility: visible;
}
img::after {
/* 黑色alt信息条 */
content: attr(alt);
position: absolute;
left: 0; bottom: 0;
width: 100%;
line-height: 30px;
background-color: rgba(0,0,0,.3);
color: white;
text-align: center;
font-size: 14px;
transform: translateY(100%);
/* 来点过渡动画效果 */
transition: transform .2s;
visibility: visible;
}
img:hover::after {
transform: translateY(0);
}
</style>
</head>
<body>
<div class="wrapper">
<img alt="facebook" data-src="img/timg.jpg">
<p><button>设置src属性显示图片</button></p>
</div>
<script type="text/javascript">
var eleButton = document.querySelector('button'),
eleImg = document.querySelector('img');
if (eleButton && eleImg) {
var initValueButton = eleButton.innerHTML;
// 图片地址
var srcImage = eleImg.getAttribute('data-src');
// 移除该属性
eleImg.removeAttribute('data-src');
// 按钮点击事件
eleButton.addEventListener('click', function() {
if (this.innerHTML == initValueButton) {
this.innerHTML = '移除src属性';
// 图片显示
eleImg.setAttribute('src', srcImage);
} else {
this.innerHTML = initValueButton;
// src属性移除
eleImg.removeAttribute('src');
}
});
}
</script>
</body>
</html>
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