//此方法為file input元素的change事件 function change(){  var file = this.files[0];  var orientation;  //EXIF js 可以讀取圖片的元信息 https://github.com/exif-js/exif-js  EXIF.getData(file,function(){    orientation=EXIF.getTag(this,'Orientation');  });  var reader = new FileReader();  reader.onload = function(e) {      getImgData(this.result,orientation,function(data){      //這里可以使用校正后的圖片data了     });   }  reader.readAsDataURL(file);}

// @param {string} img 圖片的base64// @param {int} dir exif獲取的方向信息// @param {function} next 回調方法，返回校正方向后的base64function getImgData(img,dir,next){ var image=new Image(); image.onload=function(){  var degree=0,drawWidth,drawHeight,width,height;  drawWidth=this.naturalWidth;  drawHeight=this.naturalHeight;  //以下改變一下圖片大小  var maxSide = Math.max(drawWidth, drawHeight);  if (maxSide > 1024) {    var minSide = Math.min(drawWidth, drawHeight);    minSide = minSide / maxSide * 1024;    maxSide = 1024;    if (drawWidth > drawHeight) {      drawWidth = maxSide;      drawHeight = minSide;    } else {      drawWidth = minSide;      drawHeight = maxSide;    }  }  var canvas=document.createElement('canvas');  canvas.width=width=drawWidth;  canvas.height=height=drawHeight;   var context=canvas.getContext('2d');  //判斷圖片方向，重置canvas大小，確定旋轉角度，iphone默認的是home鍵在右方的橫屏拍攝方式  switch(dir){    //iphone橫屏拍攝，此時home鍵在左側    case 3:      degree=180;      drawWidth=-width;      drawHeight=-height;      break;    //iphone豎屏拍攝，此時home鍵在下方(正常拿手機的方向)    case 6:      canvas.width=height;      canvas.height=width;       degree=90;      drawWidth=width;      drawHeight=-height;      break;    //iphone豎屏拍攝，此時home鍵在上方    case 8:      canvas.width=height;      canvas.height=width;       degree=270;      drawWidth=-width;      drawHeight=height;      break;  }  //使用canvas旋轉校正  context.rotate(degree*Math.PI/180);  context.drawImage(this,0,0,drawWidth,drawHeight);  //返回校正圖片  next(canvas.toDataURL("image/jpeg",.8)); } image.src=img;}