根据屏幕大小，加载不同大小的图片_html/css

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根据屏幕大小，加载不同大小的图片_html/css_WEB-ITnose

ringa_lee

May 14, 2018 pm 03:34 PM

引言今天要介绍的东西，很简单，但是对于前端响应式的时候是个很重要的知识；我们在用bootstrap这类前端框架时，虽然页面局部通过media query实现了，页面始终无滚动条，响应式页面。但是，bootstrap里面的img-responsive类只是通过设置图片100%，并没有真正的实现在手机上和电脑端加载不同大小的图片。
代码其实很简单

<!DOCTYPE html><html><head>    
<meta charset="UTF-8">    
<meta name="viewport" content="width=device-width,initial-scale=1">    
<title>Document</title>    
<script>        
document.createElement( "picture" );       
</script></head><body>    
<picture>            
<source srcset="pic1.png" media="(max-width: 600px)">            
<source srcset="pic2.png" media="(max-width: 800px)">            
<img srcset="pic3.png" alt="pic">        
</picture></body></html>

下面是在浏览器中的结果，我们打开Chrome浏览器，按f12后查看网络请求。

首先是三张图片

pic1.png

默认情况下，屏幕全屏，宽度大于800

pic2.png

当页面宽度在600px-800px（(600,800]）之间时

pic3.png

最后是页面小于等于600px

pic4.png

针对上面的代码，我们解释一下：其中的img元素是默认情况下显示的图片源，在其上面的两个source元素则是在特定媒体查询（media queries）条件下显示的图片。

这样我们只需要通过像写熟悉的css的媒体查询一样写代码，就能实现根据浏览器窗口大小，动态加载图片。在手机上，就不用加载一个电脑端才显示的大图。

GitHub上有位大神，基于以上的原则，编写了一个picfill的项目，大家有兴趣的可以去git上查看。

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