HTML5移动开发图片压缩上传功能

var fileReader = new FileReader();
fileReader.onload = function() {
 var url = this.result;
}
//or
fileReader.onload = function(e) {
 var url = e.target.result;
}

fileEle.onchange = function() {
 if (!this.files.length) return;
 //以下考虑的是单图情况
 var _ua = window.navigator.userAgent;
 var _simpleFile = this.files[0];
 //判断是否为图片
 if (!/\/(?:jpeg|png|gif)/i.test(_simpleFile.type)) return;
 //插件exif.js获取ios图片的方向信息
 var _orientation;
 if(_ua.indexOf('iphone') > 0) {
 EXIF.getData(_simpleFile,function(){
 _orientation=EXIF.getTag(this,'Orientation');
 });
 }
 //1.读取文件，通过FileReader，将图片文件转化为DataURL，即data:img/png;base64，开头的url，可以直接放在image.src中;
 var _reader = new FileReader(),
 _img = new Image(),
 _url;
 _reader.onload = function() {
 _url = this.result;
 _img.url = _url;
 _img.onload = function () {
 var _data = compress(_img);
 uploadPhoto(_data, _orientation);
 };
 };
 _reader.readAsDataURL(_simpleFile);
};

/**
 * 计算图片的尺寸，根据尺寸压缩
 * 1. iphone手机html5上传图片方向问题，借助exif.js
 * 2. 安卓UC浏览器不支持 new Blob()，使用BlobBuilder
 * @param {Object} _img 图片
 * @param {Number} _orientation 照片信息
 * @return {String} 压缩后base64格式的图片
 */
function compress(_img, _orientation) {
 //2.计算符合目标尺寸宽高值，若上传图片的宽高都大于目标图，对目标图等比压缩；如果有一边小于，对上传图片等比放大。
 var _goalWidth = 750, //目标宽度
 _goalHeight = 750, //目标高度
 _imgWidth = _img.naturalWidth, //图片宽度
 _imgHeight = _img.naturalHeight, //图片高度
 _tempWidth = _imgWidth, //放大或缩小后的临时宽度
 _tempHeight = _imgHeight, //放大或缩小后的临时宽度
 _r = 0; //压缩比
 if(_imgWidth === _goalWidth && _imgHeight === _goalHeight) {
 } else if(_imgWidth > _goalWidth && _imgHeight > _goalHeight) {//宽高都大于目标图，需等比压缩
 _r = _imgWidth / _goalWidth;
 if(_imgHeight / _goalHeight < _r) {
 _r = _imgHeight / _goalHeight;
 }
 _tempWidth = Math.ceil(_imgWidth / _r);
 _tempHeight = Math.ceil(_imgHeight / _r);
 } else {
 if(_imgWidth < _goalWidth && _imgHeight < _goalHeight) {//宽高都小于
 _r = _goalWidth / _imgWidth;
 if(_goalHeight / _imgHeight < _r) {
 _r = _goalHeight / _imgHeight;
 }
 } else {
 if(_imgWidth < _goalWidth) { //宽小于
 _r = _goalWidth / _imgWidth;
 } else{ //高小于
 _r = _goalHeight / _imgHeight;
 }
 }
 _tempWidth = Math.ceil(_imgWidth * _r);
 _tempHeight = Math.ceil(_imgHeight * _r);
 }
 //3.利用canvas对图片进行裁剪，等比放大或缩小后进行居中裁剪
 var _canvas = e._$get('canvas-clip');
 if(!_canvas.getContext) return;
 var _context = _canvas.getContext('2d');
 _canvas.width = _tempWidth;
 _canvas.height = _tempHeight;
 var _degree;
 //ios bug，iphone手机上可能会遇到图片方向错误问题
 switch(_orientation){
 //iphone横屏拍摄，此时home键在左侧
 case 3:
 _degree=180;
 _tempWidth=-_imgWidth;
 _tempHeight=-_imgHeight;
 break;
 //iphone竖屏拍摄，此时home键在下方(正常拿手机的方向)
 case 6:
 _canvas.width=_imgHeight;
 _canvas.height=_imgWidth; 
 _degree=90;
 _tempWidth=_imgWidth;
 _tempHeight=-_imgHeight;
 break;
 //iphone竖屏拍摄，此时home键在上方
 case 8:
 _canvas.width=_imgHeight;
 _canvas.height=_imgWidth; 
 _degree=270;
 _tempWidth=-_imgWidth;
 _tempHeight=_imgHeight;
 break;
 }
 if(window.navigator.userAgent.indexOf('iphone') > 0 && !!_degree) {
 _context.rotate(_degree*Math.PI/180);
 _context.drawImage(_img, 0, 0, _tempWidth, _tempHeight); 
 } else {
 _context.drawImage(_img, 0, 0, _tempWidth, _tempHeight);
 }
 //toDataURL方法，可以获取格式为"data:image/png;base64,***"的base64图片信息；
 var _data = _canvas.toDataURL('image/jpeg');
 return _data;
}

/**
 * 上传图片到NOS
 * @param {Object} _blog Blob格式的图片
 * @return {Void}
 */
function uploadPhoto(_data) {
 //4.获取canvas中的图片信息
 //window.atob方法将其中的base64格式的图片转换成二进制字符串；若将转换后的值直接赋值给Blob会报错，需Uint8Array转换：最后创建Blob对象；
 _data = _data.split(',')[1];
 _data = window.atob(_data);
 //如果不用ArrayBuffer,发送给服务器的图片格式是[object Uint8Array],上传失败...
 var _buffer = new ArrayBuffer(_data.length);
 var _ubuffer = new Uint8Array(_buffer);
 for (var i = 0; i < _data.length; i++) {
 _ubuffer[i] = _data.charCodeAt(i);
 }
 // 安卓 UC浏览器不支持 new Blob()，使用BlobBuilder
 var _blob;
 try {
 _blob = new Blob([_buffer], {type:'image/jpeg'});
 } catch(ee) {
 window.BlobBuilder = window.BlobBuilder || window.WebKitBlobBuilder || window.MozBlobBuilder || window.MSBlobBuilder;
 if (ee.name == 'TypeError' && window.BlobBuilder) {
 var _bb = new BlobBuilder();
 _bb.append(_buffer);
 _blob = _bb.getBlob('image/jpeg');
 }
 }
 var _suffix = 'jpg';
 if(_blob.type === 'image/jpeg') {
 _suffix = 'jpg';
 }
 //获取NOStoken
 this.__cache._$requestDWRByGet({url: 'ImageBean.genTokens',param: [_suffix,'','','','1'],onload: function(_tokens) {
 _tokens = _tokens || [];
 var _token = _tokens[0];
 if(!_token || !_token.objectName || !_token.uploadToken){
 alert('token获取失败！');
 return false;
 }
 //上传图片到NOS
 var _objectName = _token.objectName,
 _uploadToken = _token.uploadToken,
 _bucketName = _token.bucketName;
 var _formData = new FormData();
 _formData.append('Object', _objectName);
 _formData.append('x-nos-token', _uploadToken);
 _formData.append('file',_blob);
 var _xhr;
 if (window.XMLHttpRequest) {
 _xhr = new window.XMLHttpRequest();
 } else if (window.ActiveXObject) {
 _xhr = new ActiveXObject("Microsoft.XMLHTTP");
 }
 _xhr.onreadystatechange = function() {
 if(_xhr.readyState === 4) {
 if((_xhr.status >= 200 && _xhr.status < 300) || _xhr.status === 304) {
 var _imgurl = "http://nos.netease.com/" + _bucketName + "/" + _objectName + "?imageView";
 var _newUrl = mb.x._$imgResize(_imgurl, 750, 750, 1, true);
 window.location.href = 'http://www.lofter.com/act/taxiu?op=effect&originImgUrl=' + _newUrl;
 }
 }
 };
 _xhr.open('POST', 'http://nos.netease.com/' + _bucketName, true);
 _xhr.send(_formData);
 }});
}