<!DOCTYPE html>
<html lang="en">
<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>使用FormData上传压缩裁剪后的图片Blob对象</title>
</head>
<body>
<input type="file" name="myfile" id="myfile" onchange="uploadHandler(event)">
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<script>
function uploadHandler(e) {
var files = e.target.files || e.dataTransfer.files;
if (files && files.length > 0) {
var file = files[0];
resizeImage(file).then(function (result) {
return typeof result === 'string' ? convertToBlob(result, file.type) : result;
}).then(function (blob) {
// 构建FormData
var formData = new FormData();
//注意：此处第3个参数最好传入一个带后缀名的文件名，否则很有可能被后台认为不是有效的图片文件
formData.append("file", blob, file.png);
// 上传文件
$.ajax({
url: '/api/upload',
method: "POST",
data: formData,
cache: false,
processData: false,
contentType: false
}).then(function (res) {
console.log(res);
}).catch(function (err) {
console.log(err);
})
});
}
}
/**
* 压缩裁剪图片
*/
function resizeImage(file) {
return new Promise(function (resolve, reject) {
var reader = new FileReader();
reader.onload = function () {
var img = new Image();
img.onload = function () {
var w = this.naturalWidth;
var h = this.naturalHeight;
var maxW = 500;
var maxH = 500;
// 如果图片尺寸小于最大限制，则不压缩直接上传
if (w <= maxW && h <= maxH) {
resolve(file);
return;
}
var level = 0.6;
var multiple = Math.max(w / maxW, h / maxH);
var resizeW = w / multiple;
var resizeH = h / multiple;
var canvas = document.createElement("canvas");
canvas.width = resizeW;
canvas.height = resizeH;
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0, resizeW, resizeH);
var base64Img = canvas.toDataURL(file.type, level);
var arr = base64Img.split(",");
resolve(arr[1]);
};
img.src = this.result;
};
reader.readAsDataURL(file);
});
}
/**
* 将图片的base64字符串转换为Blob对象
*/
function convertToBlob(base64Str, fileType) {
var base64 = window.atob(base64Str);
var len = base64.length;
var buff = new ArrayBuffer(len);
var uarr = new Uint8Array(buff);
for (var i = 0; i < len; i++) {
uarr[i] = base64.charCodeAt(i);
}
var blob = null;
try {
blob = new Blob([buff], { type: fileType });
} catch (e) {
var BlobBuilder = window.BlobBuilder = (
window.BlobBuilder ||
window.WebKitBlobBuilder ||
window.MozBlobBuilder ||
window.MSBlobBuilder
);
if (e.name === "TypeError" && BlobBuilder) {
var builder = new BlobBuilder();
builder.append(buff);
blob = builder.getBlob(fileType);
}
}
return blob;
}
</script>
</body>
</html>