function photoCompress(file, w, objDiv) {
var ready = new FileReader();
/*開始讀取指定的Blob對象或File對象中的內(nèi)容. 當(dāng)讀取操作完成時(shí),readyState屬性的值會(huì)成為DONE,如果設(shè)置了onloadend事件處理程序,則調(diào)用之.同時(shí),result屬性中將包含一個(gè)data: URL格式的字符串以表示所讀取文件的內(nèi)容.*/
ready.readAsDataURL(file);
ready.onload = function() {
var re = this.result;
canvasDataURL(re, w, objDiv);
}
};
function canvasDataURL(path, obj, callback) {
var img = new Image();
img.src = path;
img.onload = function() {
var that = this;
// 默認(rèn)按比例壓縮
var w = that.width,
h = that.height,
scale = w / h;
w = obj.width || w;
h = obj.height || (w / scale);
var quality = 0.5; // 默認(rèn)圖片質(zhì)量為0.7
//生成canvas
var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
// 創(chuàng)建屬性節(jié)點(diǎn)
var anw = document.createAttribute("width");
anw.nodeValue = w;
var anh = document.createAttribute("height");
anh.nodeValue = h;
canvas.setAttributeNode(anw);
canvas.setAttributeNode(anh);
ctx.drawImage(that, 0, 0, w, h);
// 圖像質(zhì)量
if(obj.quality && obj.quality <= 1 && obj.quality > 0) {
quality = obj.quality;
}
// quality值越小，所繪制出的圖像越模糊
var base64 = canvas.toDataURL('image/jpeg', quality);
// 回調(diào)函數(shù)返回base64的值
callback(base64);
}
}
function convertBase64UrlToBlob(urlData) {
var arr = urlData.split(','),
mime = arr[0].match(/:(.*?);/)[1],
bstr = atob(arr[1]),
n = bstr.length,
u8arr = new Uint8Array(n);
while(n--) {
u8arr[n] = bstr.charCodeAt(n);
}
return new Blob([u8arr], {
type: mime
});
}

<form action="file/uploadDoc" enctype="multipart/form-data" method="post" id="form">
<input type="file" id="file" name="file" />
<input type="submit" value="上傳" />
</form>

$("#file").change(function() {
var formData = new formData("form");
var file = this.files[0];
photoCompress(file, {
quality: 0.5,
}, function(base64Codes) {
var bl = convertBase64UrlToBlob(base64Codes);
formData.set("file", bl, file.name);
});
});

<form enctype="multipart/form-data" method="post" id="form">
<input type="file" id="file" name="file" />
<input type="button" value="上傳" id="uploadBtn"/>
</form>

$("#uploadBtn").click(function () {
var formData = new formData("form");
$.ajax({
type:"post",
url:"",
async:true,
data:formData,
success:function (data) {
},
error:function (e) {
}
});
});

<button type="button" class="layui-btn" id="upImg">上傳圖片</button>
<div id="img_list">
</div>
<input type="button" id = "btnHide" class="none">

layui.use('upload', function() {
var upload = layui.upload;
var uploadInst = upload.render({
elem: '#upImg',
url: '/upload/',
auto: false,
bindAction: "#btnHide",
choose: function(obj) {
var files = obj.pushFile();
var index, file, indexArr = [];
for(index in files) {
indexArr.push(index);
};
var iaLen = indexArr.length;
file = files[indexArr[iaLen - 1]];
for(var i = 0; i < iaLen - 1; i++) {
delete files[indexArr[i]];
}
try {
if(file.size > 200 * 1024) {
delete files[index];
photoCompress(file, {
quality: 0.5,
}, function(base64Codes) {
var bl = convertBase64UrlToBlob(base64Codes);
obj.resetFile(index, bl, file.name);
$("#btnHide").trigger("click");
});
} else {
$("#btnHide").trigger("click");
}
} catch(e) {
$("#btnHide").trigger("click");
}
},
done: function(res) {
//這里把后臺返回的數(shù)據(jù)進(jìn)行操作，展示上傳完成的圖片，具體數(shù)據(jù)格式參考layui的API
},
error: function() {
}
});
});