JS图片压缩
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<input type="file" id="file1" onchange="selFile()" />
<img id="res" />
<script>
var maxWidth = 400;
var maxHeight =400;
var canvas = document.createElement(‘canvas‘);
var context = canvas.getContext(‘2d‘);
function selFile()
{
var file = null;
var reader = new FileReader();
var img = new Image();
//获取选中的文件
file = file1.files[0];
reader.readAsDataURL(file);
reader.onload=function(e)
{
var base64 = reader.result.split(‘,‘)[1];
var dataUrl = ‘data:image/png;base64,‘ + base64;
img.src = dataUrl;
}
img.onload = function () {
var originWidth = this.width;
var originHeight = this.height;
var targetWidth = originWidth;
var targetHeight = originHeight;
if (originWidth > maxWidth || originHeight > maxHeight) {
if (originWidth / originHeight > maxWidth / maxHeight) {
// 更宽，按照宽度限定尺寸
targetWidth = maxWidth;
targetHeight = Math.round(maxWidth * (originHeight / originWidth));
} else {
targetHeight = maxHeight;
targetWidth = Math.round(maxHeight * (originWidth / originHeight));
}
}
/////////////////// canvas
canvas.width = targetWidth;
canvas.height = targetHeight;
context.clearRect(0, 0, targetWidth, targetHeight);
context.drawImage(img, 0, 0, targetWidth, targetHeight);
var base64 = canvas.toDataURL(‘image/jpeg‘, 0.8);
res.src = base64;
/////////////////// canvas
}
}
</script>
</div>
</form>
</body>
</html>
原文：https://www.cnblogs.com/mqingqing123/p/12341712.html