检查浏览器是否支持webp
部分浏览器支持webp，部分浏览器不支持webp，下面用代码来检查下浏览器是否支持webp，方便决定让浏览器加载服务器的webp文件，还是jpg文件
测试记录 2020.02.28
1. MAC系统 Chrome Version 79.0.3945.130 (Official Build) (64-bit) 返回true
2. MAC系统 Safari 13.0.5 返回 false
3. MAC Firefox 60.9.0esr (64 位) 返回false
4. Windows Firefox 56.0.1 (64位) 返回false
5. Windows Firefox 73.0.1 (64位) 返回true
方法1：Google官方写法
这里提供了几种webp的图片模式，如果浏览器支持webp，那么图片的宽高会大于0，从而返回true,否则返回false.
第一个参数feature可以传 lossy,lossless,alpha,animation中的一个，第一个传个回调函数。获取他result。如果支持，返回ture,否则返回false。可以再谷歌和IE下试试，谷歌返回ture，IE返回false
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>测试WEBP支持</title>
</head>
<body>
<div id="msg"></div>
</body>
<script>
function check_webp_feature(feature, callback) {
var kTestImages = {
lossy: "UklGRiIAAABXRUJQVlA4IBYAAAAwAQCdASoBAAEADsD+JaQAA3AAAAAA",
lossless: "UklGRhoAAABXRUJQVlA4TA0AAAAvAAAAEAcQERGIiP4HAA==",
alpha: "UklGRkoAAABXRUJQVlA4WAoAAAAQAAAAAAAAAAAAQUxQSAwAAAARBxAR/Q9ERP8DAABWUDggGAAAABQBAJ0BKgEAAQAAAP4AAA3AAP7mtQAAAA==",
animation: "UklGRlIAAABXRUJQVlA4WAoAAAASAAAAAAAAAAAAQU5JTQYAAAD/////AABBTk1GJgAAAAAAAAAAAAAAAAAAAGQAAABWUDhMDQAAAC8AAAAQBxAREYiI/gcA"
};
var img = new Image();
img.onload = function () {
var result = (img.width > 0) && (img.height > 0);
callback(feature, result);
};
img.onerror = function () {
callback(feature, false);
};
img.src = "data:image/webp;base64," + kTestImages[feature];
}
check_webp_feature('lossless',function(feature,result){
document.getElementById("msg").innerHTML = "isSupportWebp: " + result;
});
</script>
</html> |
方法2: 生成一个图片来检查
<body>
<div id="msg"></div>
</body>
<script>
//备注，JS 代码比如放在<div id="msg"></div> 下方，
//如果放在上方在 Safari 下报错，在chrome下不报错
const supportsWebp = ({ createImageBitmap, Image }) => {
if (!createImageBitmap || !Image) return Promise.resolve(false);
return new Promise(resolve => {
const image = new Image();
image.onload = () => {
createImageBitmap(image)
.then(() => {
resolve(true);
})
.catch(() => {
resolve(false);
});
};
image.onerror = () => {
resolve(false);
};
image.src = 'data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAfQ//73v/+BiOh/AAA=';
});
};
const webpIsSupported = () => {
let memo = null;
return () => {
if (!memo) {
memo = supportsWebp(window);
}
return memo;
};
};
webpIsSupported()().then(res => {
//console.log("是否支持 webp", res)
document.getElementById("msg").innerHTML = "是否支持 webp: " + res;
}).catch(err => {
//console.log(err)
document.getElementById("msg").innerHTML = "err: " + err;
})
</script> |
方法3: 加载canvas的方法来检查，比较简洁
<body>
<div id="msg"></div>
</body>
<script>
var isSupportWebp = function () {
try {
return document.createElement('canvas').toDataURL('image/webp', 0.5).indexOf('data:image/webp') === 0;
} catch(err) {
return false;
}
}
document.getElementById("msg").innerHTML = "isSupportWebp: " + isSupportWebp();
</script> |
方法4: 利用浏览器的支持情况，后端检查
利用服务端程序判断HTTP_ACCEPT这个值 php代码为例子
<?php $str = $_SERVER['HTTP_ACCEPT']; $result = 'NO'; if(strstr($str, 'image/webp')!=false){ $result = "YES"; } echo $str; echo "<br />is support webp : ".$result; ?> |
我支持的chrome返回
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9 is support webp : YES |
我不支持的Firefox 返回
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 is support webp : NO |
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