参考网上的用法，下面是利用canvas进行的图片压缩
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta content="width=device-width,initial-scale=1.0,maximum-scale=1.0,user-scalable=no" name="viewport">
<meta content="yes" name="apple-mobile-web-app-capable">
<meta content="black" name="apple-mobile-web-app-status-bar-style">
<meta content="telephone=no" name="format-detection">
<meta content="email=no" name="format-detection">
<title>slip</title>
<style>
*{padding: 0;margin: 0;}
</style>
</head>
<body>
<div class="input">
<input type="file" id="file" accept="image/*">
</div>
</body>
<script type="text/javascript">
var img=new Image();
var reader=new FileReader();
// 选择的文件对象
var file = null;
var eleFlile=document.querySelector('#file');
var canvas=document.createElement('canvas');
var context=canvas.getContext('2d');
img.onload=function () {
//图片原始大小
var originWidth = this.width;
var originHeight = this.height;
//限制图片大小
var maxWidth = 400;
var maxHeight = 400;
var targetWidth = originWidth, targetHeight = originHeight;
if (originHeight > maxHeight || originWidth > maxWidth) {
if (originWidth / originHeight > maxWidth / maxHeight) {
//更宽
targetWidth = maxWidth;
targetHeight = Math.round(maxWidth * (originHeight / originWidth));
} else {
//更高
targetHeight = maxHeight;
targetWidth = Math.round(targetHeight * (originWidth / originHeight))
}
}
//图片缩放
canvas.width = targetWidth;
canvas.height = targetHeight;
//清除画布
context.clearRect(0, 0, targetWidth, targetHeight);
//图片压缩
context.drawImage(img, 0, 0, targetWidth, targetHeight);
//转换上传toBlob
canvas.toBlob(function (blob) {
//图片ajax上传
var xhr=new XMLHttpRequest();
//文件上传成功
xhr.onreadystatechange=function () {
if(xhr.status==200){
alert("上传成功")
}
};
xhr.open("POST","upload.php",true);
xhr.send(bolb);
} ,file.type || 'image/png');
var newImg = document.createElement("img"),
url = URL.createObjectURL(blob);
newImg.onload = function () {
// no longer need to read the blob so it's revoked
URL.revokeObjectURL(url);
};
newImg.src = url;
document.body.appendChild(newImg);
// })
//图片上传toDataURL
var url=canvas.toDataURL();
var newImg = document.createElement("img")
newImg.src = url;
document.body.appendChild(newImg);
}
//文件base64化
reader.onload=function (e) {
img.src=e.target.result;
};
eleFlile.addEventListener("change",function (event) {
file=event.target.files[0];
if(file.type.indexOf("image")==0){
reader.readAsDataURL(file);
}else {
alert("请传图片")
}
})
</script>
</html>