H5移动端图片压缩上传开发流程

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);
 }});
}